For most people, bones stop growing in length between ages 14 and 20, depending on sex and which bone you’re looking at. Girls typically finish earlier, with most growth plates closing by 14 to 16, while boys finish closer to 16 to 20. But a few bones, particularly the collarbone, can continue growing into your mid-20s.
How Growth Plates Work
Every long bone in your body, from your thighbone to the small bones in your fingers, grows from a strip of cartilage near each end called a growth plate. This cartilage contains specialized cells called chondrocytes that multiply rapidly during childhood and adolescence, stacking on top of each other like coins in a roll. As new cartilage cells form at one end, older cells at the other end die off and are gradually replaced by blood vessels and bone-building cells. The result is that the bone gets longer, bit by bit, pushing you taller.
Once the cartilage cells in a growth plate have used up their ability to divide, the entire strip of cartilage gets replaced by solid bone. This is called fusion, and it’s essentially permanent. On an X-ray, an open growth plate appears as a dark gap near the end of a bone. When it fuses, that gap disappears, and doctors can tell that growth at that site is finished.
The Timeline Differs by Sex
Girls generally hit their growth milestones one to two years ahead of boys, which mirrors the earlier onset of puberty. In the knee, where some of the body’s most important growth plates sit, initial fusion has been observed as early as age 14 in girls and 16 in boys. Full fusion of the knee tends to wrap up around age 21 for girls and 24 for boys. Hand and wrist bones follow a similar pattern, finishing around 17 to 21 in girls and 20 to 23 in boys.
These are averages, and individual variation is real. Genetics, nutrition, and the timing of puberty all shift the window. But the general rule holds: if you’re female, most of your height growth is done by your late teens. If you’re male, you may gain small amounts into your early 20s.
Why Estrogen Is the Real Off Switch
The hormone that ultimately shuts down your growth plates is estrogen, and this is true for both sexes. Testosterone matters too, but largely because the body converts some of it into estrogen. Rising estrogen levels during puberty initially fuel the adolescent growth spurt by stimulating the cartilage cells to multiply faster. But estrogen also accelerates the aging process within those cells, wearing out their ability to divide.
Research published in the Proceedings of the National Academy of Sciences showed that estrogen doesn’t directly turn cartilage into bone. Instead, it speeds up a built-in countdown. Growth plate cartilage cells have a limited number of divisions available to them, almost like a biological clock. Estrogen makes that clock tick faster, exhausting the cells’ capacity to reproduce sooner. Once proliferation drops to essentially zero, fusion happens rapidly. All the remaining cartilage gets replaced by bone in a relatively sudden event.
This explains why children who enter puberty unusually early (a condition called precocious puberty) often end up shorter as adults. The early surge of estrogen triggers a dramatic growth spurt, but it also burns through the growth plates’ remaining capacity years ahead of schedule. The growing period gets cut short, and the final adult height suffers.
The Collarbone: The Last Bone to Finish
Even after most of your skeleton has fused, the collarbone keeps going. The growth plate on its inner end (closest to your sternum) doesn’t fuse until roughly 23 to 25 years of age. Research from Hospital for Special Surgery found substantial collarbone growth potential after age 18, with remodeling still occurring up to age 25. In their study, growth was still ongoing in many of the oldest participants, meaning the true endpoint was hard to pin down.
This doesn’t translate to getting taller, since the collarbone grows in width and length across the shoulders rather than vertically. But it does mean your skeletal development isn’t truly complete until your mid-20s.
Growing Taller vs. Growing Stronger
There’s an important distinction between bones growing longer (which makes you taller) and bones growing denser (which makes them stronger). Growth plate fusion ends your height gain, but your skeleton continues to add mineral density for years afterward. Peak bone mass, the point at which your bones are at their densest and strongest, arrives in the early to late 20s. Women typically reach peak bone density around age 22, while men reach it closer to age 27.
After that peak, your bones don’t stop changing. They undergo a lifelong process called remodeling, where old or damaged bone tissue gets broken down and replaced with new bone. This keeps your skeleton healthy and responsive to the physical demands you place on it. Weight-bearing exercise and adequate calcium and vitamin D intake during the teens and 20s help maximize that peak, giving you a larger reserve to draw from as you age.
What Can Delay or Speed Up the Timeline
Nutrition plays a significant role. Chronic malnutrition, whether from poverty, eating disorders, or digestive conditions like celiac disease, can slow or temporarily halt linear growth. Children with anorexia nervosa, for instance, show measurable stunting even when their height was normal before the illness began. If nutrition improves, the body can partially catch up through a period of accelerated growth, but this recovery is often incomplete, and some height is permanently lost.
On the other end, conditions that cause excess growth hormone or delayed puberty can extend the growth window, leading to taller stature but also potential complications. The interplay between when puberty starts and how long the growth plates stay open is what ultimately determines adult height. An earlier puberty compresses the timeline. A later puberty extends it.
Why Your Nose and Ears Keep Changing
You may have noticed that older adults seem to have larger noses and ears. This isn’t bone growth. After your growth plates fuse, your bones no longer get longer. What does change is cartilage and soft tissue. The cartilage in your nose and ears weakens over time, and gravity gradually pulls it downward. The tip of the nose droops, a process called nasal tip ptosis, because cartilage loses its structural support while the bone above it stays put. Skin also loses elasticity, which makes ears appear to sag. These changes are a normal part of aging, not a sign that your skeleton is still growing.