"we skip entirely over the value of working for large, established companies before you create your own."
When I first started writing about startups, I believed this. I suggested that would-be founders work for a couple years for existing companies before trying to start their own. But the empirical evidence changed my opinion. You can learn things from working at an existing company, certainly, but you learn more from trying to start a startup.
It seems beneficial to have at least some experience with working at an existing company. Knowing how things are traditionally done, knowing where the bottlenecks and communication problems lie, can be a big help in figuring out where you can take advantage of your own situation. It also helps you not take for granted many of the more subtle benefits a startup provides.
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.
When I first started writing about startups, I believed this. I suggested that would-be founders work for a couple years for existing companies before trying to start their own. But the empirical evidence changed my opinion. You can learn things from working at an existing company, certainly, but you learn more from trying to start a startup.