I know a bunch of people at Google who started programming in college. I also knew a few people in college who started there and are now getting CS Ph.Ds.
Curiously, it seems to be mostly women who are good devs and yet didn't start until college. I'm not really sure what to make of that. Could be selection bias - since boys are encouraged to play with computers, most of the ones who will be any good at it started in grade school, while since girls have no such encouragement, even ones that are good at it may never have discovered that until college. Or it could be that all boys who are good at computers let it take over their life, and girls have many competing interests. Or it could that only girls have the discipline to become good at something without it becoming their life.
Curiously, it seems to be mostly women who are good devs and yet didn't start until college. I'm not really sure what to make of that. Could be selection bias - since boys are encouraged to play with computers, most of the ones who will be any good at it started in grade school, while since girls have no such encouragement, even ones that are good at it may never have discovered that until college. Or it could be that all boys who are good at computers let it take over their life, and girls have many competing interests. Or it could that only girls have the discipline to become good at something without it becoming their life.