Having worked at both small and big companies, I can say you can learn a lot of different things at both. Diversity of experience is valuable.

Speaking of YC, I'd love to have a Y Combinator for older, more established folks with track records....

A lot of the structure doesn't support older founders. E.g.: "We’ll invest $125k in return for 7% of your company using a 'post-money' Simple Agreement for Future Equity (the 'YC Safe'). We think that $125k is currently the right amount for founders to be able to run their company and pay expenses for around 5-6 months, and sometimes even longer."

$125k will support a team straight out of college. It won't support a team at a stage of their life when they have e.g. families or kids.