I'm in my early 40s, I can't really think of anything, maybe because it's too close to realize what mistakes I might have made, and I don't really believe in that kind of retrospection generally.
FWIW, if you are in a position where you could potentially start a family (and want to some day), consider doing it in your early 30s (or earlier), there are a lot of things that get tougher as you get older. I don't regret putting it off until my 40s because it let me find a person I want to have a family with, but if you have such a person, my advice is do it now.
FWIW, if you are in a position where you could potentially start a family (and want to some day), consider doing it in your early 30s (or earlier), there are a lot of things that get tougher as you get older. I don't regret putting it off until my 40s because it let me find a person I want to have a family with, but if you have such a person, my advice is do it now.