Our body grows with the help of proteins. The proteins get converted into amino acids during the process of digestion. The cells and tissues are produced by these amino acids. Proteins along with minerals produce and repair muscles, tissues and bones.
Growth of our body is controlled by the endocrine glands that we have. After a certain age, the body gets the full maturity. It takes too much food and energy to keep on growing after we have hit maturity. So after maturity, the body stops growing up, because after this age the glands which are responsible for growth become less active. But there is very slow continuous growth.