My dad, who once applied to YC, said that YC favours founders between ages 25-35. Not too young to be inexperienced, not too old to have other obligations.
I was going to say the funding isn't enough for anyone who isn't young but then I looked at the Y Combinator Deal: "We invest $500,000 in every company on standard terms."
I got an interview at 33 years old last year. Curious how old the oldest person they interviewed was. I imagine they are looking for an intersection between age for energy, and experience for success.