I( worked as a developer for a startup aged 34 ... in the UK. I was the youngest person in the startup, too. (It went public via reverse-takeover and ended up being absorbed by Mastercard a decade later: as we were in payment services, you could consider this a win.)

There is an elephant in the room that the Americans on HN are reluctant to admit, which is that the US healthcare system sucks. Startups can't easily afford the corporate health insurance premiums they need in order to attract older staff, so they perforce rely on the young and healthy — who are cheaper, don't have families, and don't have expensive chronic conditions.

The US healthcare system thus applies invisible constraints to hiring practices that encourage unspoken discrimination against experienced adults.

(Whereas in the UK we had a working NHS to provide cover for us and our families, and in Germany the insurance system is at least sane. Sure, our VC and finance sector is (or was, in my day) less hospitable to startups, but: swings and roundabouts.)