When do people stop growing?

Stop growing - people stop growing when their bones do, and that is usually between 15 and 25 years of age. Bones are made up of living tissue, composed of special cells which secrete round themselves material rich in calcium salts and as hard as marble. The formation of bone (ossification) is a complex process which usually begins in cartilages (gristle). In a child the bone begins to form in the middle of the cartilage and spreads towards both ends, turning it all to bone with the exception of the tips. From these points the bone grows in length and so does the child. When the growing period is over the tips of the bones close by joining the main shaft of the bone. Bones vary greatly in shape and size. Long ones act as levers. Flat ones are centres for muscle action. But each has a cavity containing bone marrow. Around this the bony substance is spongy in texture, becoming hard nearer the surface where the calcium is densest. On the surface of the bone is a special layer of fibrous tissue (the periosteum) which is rich in bone building cells.