Congratulations! Your age might give you trouble--people will feel embarrassed to work for such young people, and people in general might not take you seriously. Good luck!
I hear there's this other guy who tried to start a social network... Zuckersomething... was pretty young too. I think things worked out pretty alright for him.
They'll be fine :) If anything, they are best positioned to appreciated exactly how Facebook doesn't work for families.
People who are concerned with the age of their boss are a little too concerned with status / authority / hierarchy to be at an early-stage startup.