Boys stop growing for a number of reasons. The most common reason for a boy to stop growing is that he has reached the end of his natural growth. Other factors also prematurely halt growth, including growth plate injuries, poor nutrition and chronic illnesses. The best way to tell if a boy has stopped growing, whether naturally or due to an external influence, is to consult a physician. There are, however, some common, identifiable signs that indicate the end of growth in boys.
One sign that growth is drawing to a close is his arrival at puberty. Growth actually accelerates temporarily at this stage in what's known as the adolescent growth spurt. Most boys hit puberty between the ages of 10 and 13. A year or two after the initiation of puberty, boys experience a doubled growth rate, resulting in a growth rate as high as 12 cm (4 inches) per year.
After one to two years of fast growth in the adolescent growth spurt, a boy's growth rate slows again. Within the next few years following the spurt, growth slows gradually, first returning to the pre-spurt average, then dropping lower. By a boy's 17th birthday, his body only has about 2.5 cm (1 inch) of total growth left to complete.
While the timelines above are generally accurate, they are not true for all boys. Growth rate differs among children, as does puberty onset. Some children grow early and fast, while other grow slowly and later than their peers. Other factors also influence growth rate, such as chronic diseases. Diseases such as Crohn's, for example, sometimes induce stopped or slowed growth earlier than the timelines given.
Fused growth plates
A tell tale indicator of stopped growth in adolescents is fusion of the growth plates. Growth plates are unfused plates on the bones that allow for expansion. Once the plates have fused, no further growth is possible. Fusion of growth plates is detected by X-ray. Different growth plates close at different times, so while a boy's wrist or feet plates have fused, it doesn't mean his growth has stopped. Height is mostly dependent on growth in the legs and spine.
Though variations in growth rate are common, sometimes a slowing of growth is a red flag indicating a growth disorder. If the boy had been growing at a normal rate and suddenly ceased growth, talk to a doctor or paediatrician. If he has a chronic condition such as Crohn's that is possibly affecting his growth rate, ask a doctor for recommendations and advice.