We stop growing because each of us is genetically programmed to do so. Our genes, inherited from our parents, determine how we grow. Science has not yet produced a precise answer as to how our genes control the growing process. Certain parts of us obviously continue to grow, and repair, until death. It is not possible to give a precise answer to your question in terms of a specific number of years as we are all different, but you could say that many people may still be growing after age 25, whilst many others will have stopped at any time before that.