Anyway, for me, it's definitely the feeling that if I screw something up I can't just "try something else next year." I've had 4 or 5 careers already, which of course means I've done exactly 0 career advancement. (I'm a SAHD now, yay! Best boss ever!)
Anyway, I'm starting to realize that an entirely fresh college degree is probably out of the question, that my chances of doing anything entirely different get smaller every year.
I think the hardest thing about being over 30 for me is the 'ticking biological clock'. All my friends are popping sproglets out all over the shop and I still can't decide if I want them or not!