I have a feeling that age doesn't matter, but lifestyle (due to commitments) is incredibly important.

the case where you not only have zero leisure time but indeed work so hard that you endanger your health.

http://www.paulgraham.com/wealth.html

If you can't work that hard due to commitments then you are going to have a hard time of it.

I guess if you don't have a family to support and don't plan on having one, you too can be an entrepreneur, no matter your age.

I'd like to take this moment to thank my patient wife and her job at Oracle...

Hey, look! I'm not too old (at 34)! :)

Randall, we're not too old, although hanging around here may give you that impression. YC focuses on younger founders because they're undervalued, not necessarily more plentiful or successful in absolute terms.