Most were early and mid twenties; they were my colleague for at most a couple of years before moving on to e.g. Google in Europe or SV startups (working from Ireland until he could get a green card). Another one was iirc late twenties / early 30's, great Scala developer - perhaps too good because his work didn't really land at our customers because they couldn't find any developers that could work with it. (that's more down to Scala than the guy though).

But I don't actually know any developer above the age of 40. If they do anything it's code challenges like Advent of Code, but they've long moved on from software development to e.g. architecture, management, coaching, etc and making more money through that - and giving off an air that they're much more content and at peace with it - than they could with software development.

I'm in my early to mid 30's myself and I'm pondering what I'd like to do beyond software development, I've had enough and ten years of making websites without an opportunity to branch out wears on you.