I was just thinking about this today. I was reflecting on how I'm giving up > $100K/yr. for a small but reasonable chance of making > $2m in ~2 years.

I agree that the opportunity cost is higher for older founders, but (as others have observed) so is the probability of success, at least vs. non-YC younger founders. It's also true that, if you are willing to live like a grad student, you can mitigate your risk by doing consulting/contract work beforehand or on the side. So could a 23-year-old, of course, but for a variety of reasons they usually don't bill at nearly as high a rate. I don't have to work very long at $100-125/hr. before I've got a year's living expenses saved up.

The real catch is if you have a family to support. I'm (un)lucky enough not to have that problem.