I probably wouldn't bother with college, but that's a tough one.
There was no educational value there that I couldn't have easily gotten on my own. Everything about it that wasn't school I remember fondly. But the actual work was stressful to the point that I still can have the occasional bad dream about being behind in schoolwork.
Professionally, I would move on from playing poker MUCH earlier than I did. If we go back with knowledge of future betting markets, trends, etc, of course I would make be able to retire in no time, but I don't think that's really the spirit of the question.
As far as interpersonal stuff goes, I'd like to think that going back, knowing what I know, I would be better to people and that would be better for me as well. Just a couple pretty large regrets that I think I could avoid the second time around, even without specific knowledge of them.