Most boys’ growth plates close between the ages of 15 and 20, with the specific timing depending on the bone in question and the individual’s pace of puberty. An MRI-based study of adolescents and young adults found that half of boys had fused growth plates at various sites between ages 15 and 18, while 90 percent had fused between ages 17 and 20, with all male subjects showing complete closure at every measured site by age 21.1PubMed Central. A cross-sectional magnetic resonance imaging study of factors influencing growth plate closure in adolescents and young adults That window is about two years later than the equivalent range for girls, and the story behind why involves hormones most people wouldn’t expect.
What a Growth Plate Actually Is
A growth plate is a strip of cartilage near the ends of long bones. It contains specialized cells called chondrocytes that go through a life cycle: they start in a resting state, then multiply rapidly, swell up, and eventually die. Once they die, blood vessels move in and the cartilage is gradually replaced by hard bone tissue. As long as that cycle keeps running, the bone keeps getting longer. When it stops, the cartilage is fully replaced, the gap on an X-ray disappears, and the plate is considered “closed” or “fused.”2PubMed Central. The growth plate: a physiologic overview At that point, no further lengthening of that bone is possible.
Estrogen, Not Testosterone, Triggers Closure
One of the most counterintuitive facts about male skeletal growth is that estrogen, not testosterone, is the hormone responsible for shutting growth plates down. Boys do produce estrogen, just in smaller quantities than girls. During puberty, an enzyme called aromatase converts a portion of testosterone into estrogen. Once estrogen levels reach a critical threshold, the pool of resting chondrocytes in the growth plate starts to deplete. Fewer resting cells means fewer cells available to proliferate and push the bone longer. Eventually the supply runs out entirely and the plate fuses.3PubMed Central. The endocrine role of estrogens on human male skeleton
This is why boys typically end up taller than girls. Boys enter puberty later, giving them roughly two extra years of pre-pubertal growth before estrogen starts closing things down. They also experience their pubertal growth spurt at a later age, so the bones have a longer runway before fusion. The end result is that both the timing of puberty’s onset and the growth rate during the pubertal spurt contribute to the height difference between males and females.
Testosterone still matters for bone development. Along with growth hormone and insulin-like growth factor 1 (IGF-1), testosterone stimulates bone modeling and increases bone density throughout puberty.4PubMed. Impact of androgens, growth hormone, and IGF-I on bone and muscle in male mice during puberty Research in boys at different pubertal stages has found that testosterone and the IGF-1 system are the major drivers of bone mineral density.5PubMed. The influence of serum ghrelin, IGF axis and testosterone on bone mineral density in boys at different stages of sexual maturity But when it comes to the specific question of when growth stops, estrogen holds the keys.
Not All Bones Close at the Same Time
Growth plate closure isn’t a single event. It’s a rolling process that starts with certain bones and ends with others, spanning several years. In general, the bones of the hands and feet tend to fuse earlier, while the long bones of the arms and legs follow, and a few stragglers keep going well into the early twenties.
During the adolescent growth spurt, the sequence is roughly predictable. The small bones of the fingers (the distal phalanges) begin fusing relatively early. By the time those finger plates start to close, a boy has already passed his peak growth velocity and is approaching about 96 percent of his adult height.6Scientific Reports. The Uniform Pattern of Growth and Skeletal Maturation during the Human Adolescent Growth Spurt Growth is nearly complete when only the growth plates at the wrist end of the radius and ulna remain open. In the shoulder, the humeral head (the ball of the upper arm bone) undergoes partial fusion on average about two years after peak height velocity, with complete fusion following roughly four years after the growth spurt’s peak.7PubMed Central. Humeral Head Ossification Predicts Peak Height Velocity Timing and Percentage of Growth Remaining in Children
This staggered sequence is useful clinically. Orthopedic surgeons and endocrinologists can look at which plates are still open and roughly estimate how much growth a boy has left, without needing to calculate exact bone age every time.
The Last Growth Plate to Close
One growth plate stands apart from the rest as a true outlier: the medial clavicular epiphysis, at the inner end of the collarbone near the sternum. In most boys, the long bone plates are done by the late teens or very early twenties. But the medial clavicle doesn’t play by the same rules. Research on this joint has found that partial union can appear anywhere from age 16 to age 26, with complete fusion first seen at age 22 and not reaching 100 percent of the population until age 27.8PubMed. Bone age determination based on the study of the medial extremity of the clavicle
This peculiarity has made the medial clavicle especially important in forensic medicine. When all other skeletal age markers have already fused and can no longer help distinguish a 19-year-old from a 25-year-old, the clavicle is the one bone that can still provide information. Forensic investigators rely on CT scans or ultrasound of this area to estimate whether someone has crossed legal age thresholds.9PubMed. Skeletal age estimation based on medial clavicle–a test of the method reliability So if you’re asking “when does every growth plate finally close in boys,” the honest answer is that most are done between 17 and 21, but the collarbone can keep going until the mid-to-late twenties.
How Doctors Check Bone Age
The standard way to assess skeletal maturity is a single X-ray of the left hand and wrist. That one image captures a lot of different bones at different stages of development, giving doctors a snapshot of where a boy’s skeleton sits on the maturation timeline.10PubMed Central. Evaluation of Bone Age in Children: A Mini-Review The two main methods for reading these X-rays are the Greulich-Pyle atlas, which compares the image to a book of reference standards, and the Tanner-Whitehouse method, which scores individual bones. The Greulich-Pyle approach is faster and more commonly used, while Tanner-Whitehouse is considered somewhat more reliable.11PubMed Central. Hand X-ray in pediatric endocrinology: Skeletal age assessment and beyond
Automated computer systems have made this process faster and more consistent. One widely used software tool, BoneXpert, was extended in 2016 to cover bone ages up to 19 years for boys, reflecting the fact that male skeletal maturation often isn’t finished at the system’s original cutoff of 17.12PubMed. Automated determination of bone age from hand X-rays at the end of puberty and its applicability for age estimation These tools are especially useful for tracking children with growth disorders, planning orthopedic surgery, or evaluating whether a boy’s growth is ahead of or behind schedule.
Bone age and calendar age don’t always match. A 14-year-old whose bone age reads as 12 still has more growing to do than his calendar age might suggest, while a 14-year-old with a bone age of 16 is closer to finished. This distinction matters a great deal for treatment decisions.
When Closure Is Delayed
Some boys are simply late bloomers. The most common reason for delayed growth plate closure is constitutional delay of growth and puberty, a condition where puberty starts later than average. These boys tend to be shorter than their peers in early adolescence and their bone age lags behind their actual age, but they keep growing after their classmates have stopped. The condition is linked to delayed skeletal maturation, an attenuated pubertal growth spurt, and relatively low levels of IGF-1.13PubMed Central. An approach to constitutional delay of growth and puberty It runs in families and in most cases resolves on its own, with adult height ending up in the normal range.
The tricky part is distinguishing constitutional delay from a more serious hormonal problem called isolated hypogonadotropic hypogonadism, where the brain doesn’t send the right signals to kick off puberty. The two conditions look very similar in the early stages, and the overlap in their clinical and hormonal features can make diagnosis difficult.14PubMed. Comparison of long-term height and pubertal outcomes in boys with delayed puberty due to constitutional delay in growth and puberty (CDGP) and isolated hypogonadotropic hypogonadism (iHH) In constitutional delay, puberty eventually begins spontaneously. In hypogonadotropic hypogonadism, it doesn’t without treatment. If a boy shows no signs of puberty by age 14, or if bone age is significantly behind, further evaluation is warranted.
Nutrition can also play a role. An inadequate diet during childhood and puberty, particularly one lacking sufficient protein, vitamins, and minerals, can stunt growth and delay the normal pace of skeletal maturation.15PubMed Central. Nutrient and Hormonal Effects on Long Bone Growth in Healthy and Obese Children: A Literature Review In well-nourished populations this is less of a concern, but globally it remains one of the leading causes of short stature.
What Happens When Estrogen Is Missing
The most dramatic illustration of estrogen’s role in male growth plate closure comes from a case reported in the New England Journal of Medicine. A man with a genetic mutation that made his estrogen receptors nonfunctional was 204 centimeters tall (about 6 feet 8 inches) and had incomplete epiphyseal closure, meaning his growth plates were still partially open despite otherwise normal pubertal development and testosterone levels.16PubMed. Estrogen resistance caused by a mutation in the estrogen-receptor gene in a man He continued to grow linearly well into adulthood. This single case reshaped the understanding of what drives growth plate fusion. Before it was published, many researchers assumed testosterone itself was the main factor in closing male growth plates. The estrogen-resistant man proved that without functional estrogen signaling, even abundant testosterone cannot finish the job.
A related group of conditions involves mutations in the aromatase gene, which prevents the conversion of testosterone to estrogen. Men with aromatase deficiency show a similar pattern: tall stature, open growth plates persisting into adulthood, and low bone density. Treatment with estrogen in these patients can induce fusion and halt further growth. These cases are extremely rare but they provide a natural experiment that confirms estrogen as the essential signal for closure.
Aromatase Inhibitors and the Question of Growing Taller
Because estrogen drives closure, blocking its production can theoretically keep growth plates open longer and allow more growth. This is the logic behind aromatase inhibitors, drugs that prevent the enzyme aromatase from converting testosterone to estrogen. Researchers have explored their use in boys with predicted short stature, and studies have shown that these drugs do slow down the rate of skeletal maturation.17PubMed. Use of aromatase inhibitors to increase final height
However, enthusiasm for this approach is tempered by safety concerns. While aromatase inhibitors may help preserve height potential by delaying fusion, the long-term effects on bone health, metabolic function, and other systems are not fully characterized. Estrogen is important for achieving peak bone density in males, not just for closing growth plates, so suppressing it during a critical window carries real risks. Reviews of the evidence have concluded that continued caution and further study are needed before aromatase inhibitors could be recommended as a routine height-boosting intervention.18PubMed Central. Aromatase inhibitors to augment height: continued caution and study required These drugs are not approved for this purpose in most countries.
Growth Plate Injuries in Young Athletes
As long as growth plates are open, they are vulnerable to injury. The cartilage of an active growth plate is softer than the surrounding bone, making it a structural weak point. In boys who participate in organized sports, both sudden traumatic injuries and chronic overuse injuries to growth plates have been reported. A systematic review of sports-related physeal injuries found that stress-related injuries to the lower extremities are a growing concern.19PubMed Central. Physeal injuries in children’s and youth sports: reasons for concern? While most growth plate injuries heal with treatment and rest, some can cause growth disturbance or limb deformity if the damage disrupts the plate’s ability to produce new cartilage evenly.
The practical takeaway for parents and coaches is that bone pain near a joint in a growing teenager should never be dismissed as “just growing pains,” especially if it’s persistent or follows a specific injury. Pain at the end of a long bone during a period of active growth warrants medical evaluation. Imaging can determine whether a growth plate is involved, and early intervention generally leads to better outcomes.
Are Today’s Boys Maturing Earlier?
There’s a popular perception that children are growing up faster than previous generations, and the skeletal data partly supports this. A comparison of hand-wrist X-rays from modern children against historical reference populations found that indicators of bone fusion were advanced by about three months in boys in the more recent cohort.20PubMed Central. Do Secular Trends in Skeletal Maturity Occur Equally in Both Sexes? That’s a measurable shift, but it’s modest. A separate study looking at biological maturation at age 14 found a significant trend toward earlier maturation over recent decades, though by age 18 the difference was no longer statistically significant.21Frontiers in Public Health. Secular trends in physical growth, biological maturation, and intelligence in children and adolescents born between 1978 and 1993
Not all studies agree, though. Research using cervical vertebrae maturation as the indicator found no evidence that boys are maturing skeletally earlier than in previous generations.22European Journal of Orthodontics. Secular trends in the timing of skeletal maturation as assessed by the cervical vertebrae maturation method The picture is complicated by the fact that different bones and different maturation indicators can shift in different directions. In the same study that found earlier fusion, indicators of bone shape in long bones were actually maturing slightly later in boys. The upshot is that while nutrition and health improvements over the past century have likely nudged some aspects of skeletal maturation earlier, the shift is measured in months, not years, and the classic age ranges for growth plate closure in boys still hold up reasonably well.
The Growth Spurt’s Relationship to Final Height
Parents often want to know not just when growth ends, but how to read the signs along the way. The adolescent growth spurt offers useful landmarks. Peak height velocity, the fastest rate of height gain, typically occurs around age 13 to 14 in boys. At the moment of peak growth, a boy has usually reached about 90 percent of his final adult height. Growth then decelerates fairly quickly: about a year and a half after the peak, he’ll be at roughly 96 percent of adult height, and the remaining four percent trickles in over the next two years or so.6Scientific Reports. The Uniform Pattern of Growth and Skeletal Maturation during the Human Adolescent Growth Spurt
For a boy who hits peak velocity at 14, this means noticeable growth continues until about 15 or 16, with smaller increments tapering off until 17 or 18. By the time only the wrist growth plates remain open, there’s very little height left to gain. This timeline fits neatly with the skeletal fusion data showing most boys completing closure between 17 and 20. The final centimeters of height are often frustratingly slow, which is why many teenage boys feel like they’ve “stopped growing” a year or two before their plates actually close.
Shoulder X-rays tell a similar story from a different angle. The humeral head reaches complete fusion on average about four years after peak height velocity.7PubMed Central. Humeral Head Ossification Predicts Peak Height Velocity Timing and Percentage of Growth Remaining in Children For a boy who peaks at 14, that puts complete shoulder fusion around 18, consistent with the general pattern of closure wrapping up in the late teens.