There are two ways in which one might be better off starting a startup than going to work for an existing company: you might learn more, and you might have high

There are two ways in which one might be better off starting a startup than going to work for an existing company: you might learn more, and you might have higher expected value. What I'm claiming (since this benefit of working for an existing company is what the OP is talking about) is that the former is almost always true. The latter, frankly, is never going to be true for more than a small percentage of people, regardless of age.