It is partially due to assortative matching. Startups don't advertise to (or maybe even want) older candidates, while many older candidates don't actually want

It is partially due to assortative matching. Startups don't advertise to (or maybe even want) older candidates, while many older candidates don't actually want to work at startups. Laying blame just on the companies doesn't quite make sense to me. Of the several hundred applicants we've gotten at Standard Treasury, the median age is likely a little less than the founding team (we're all 27-28). That age is likely even higher than most other startups that go through YC as we build enterprise software for banks -- it's not the sexiest topic in the world. Well, it is to me but you get my point. We've hired some people that skew older compared to most other startups we know but that only seems to our benefit, frankly.