That's the question making the round on the MiForum listserv today, and it's a good one. Not sure what I'd tell myself, other than:
1. Never stop learning (and everything is teaching you something, whether you know it at the time or not).
2. Stop worrying so much about what others think of you. It's what you think of yourself that really matters (and really, no one else is thinking about you as much as you think they are--they're all worrying about what you think of them. One of life's little ironies).
3. It's better to try and fail than to chicken out and regret it later. Take chances every chance you get. (See #1--failure is the best teacher of all. Learn from it whenever you can.)
4. Drive fast cars now while your reflexes and vision are good.
5. Stop beating up your body. It's got to last a while.
And, of course: This is as good-looking as you're ever going to get--flaunt it while you can!