Why do we get old?

You ask: Why we get old?

Time chip at Caveman slow, and here why. Body made of tiny cells that copy selves to mend wear — new skin, new gut, new blood. But each copy not perfect; tiny mistakes pile into the recipe over many many copies. Also, end of each DNA thread wear a little cap, like binding on a rope end — every copy the cap get shorter, and most cells can copy only about fifty times before the rope fray and cell copy no more. Body's little fire-pits (mitochondria) that make power grow weak, junk build up inside cells, repair crew slow down. Why body not fix all? Nature care most that Caveman live long enough to make young — after that, less push to keep Caveman fresh. Cave wisdom: old not one big break — old is many tiny wears piling up faster than body can mend them.