We stop growing because we are genetically programmed to. Our genes, from our parents, determine how we develop but environmental factors also affect how tall we grow. We know our DNA controls the growing process, but scientists are still unsure how our genes do this. We stop growing when we reach the age at which our bodies can reproduce. At this point, the purpose for growth is complete so our genetic control centre tells us to stop.
Answered by Louise Thomas, Science Museum.