In fact, the startups that I spoke with that were doing interesting and market-competitive things had a lot of leadership and guidance from wizened engineers and researchers - usually much older than the startup stereotype.
In the end, I think it's a startups job to shake-things-up, and approach a problem from a new angle, which is a young-man's game, but now with the calibre of thinkers working in technology, it requires some deep knowledge in a particular field. This (hopefully) comes with age.
tl;dr Yea, I've been noticing the same thing.