Earlier quoted context omitted.
Working in SV, quite honestly the best member of my team is >40 (I'm in my late 20's). I don't understand ageism at all, experience really makes the job easier and I value that wealth of knowledge as a more junior dev
The best team composition is an age of ranges, spanning 20 years- eg: early twenties to late 40s. (I wouldn't turn down an engineer older than that though, of course). And ranges of experiences. You need diversity to refine the ideas before committing them to code. Often the younger guys are faster at producing features, but produce lower quality code while the older guys understand architecture but aren't as fast at…
It's the older women who rock both architecture and quick execution. :) ("I'm sorry, but you opened the door, counselor")
Age does not immediately confer advantages or disadvantages - we just often use it as a proxy for "experienced", "more methodical", "slower", "inflexible", "good mentor". (Your pick here)
All of those are independent of age. Please don't compose a team by age. (Speaking as an older person. I bring a lot of things to the table, but my birthdate isn't one of them)