The ageism in SV has very little to do with actual talent and productivity and much more with how the team feels someone can handle themselves at happy hour.
"He's been at it for four days straight. He just re-wrote our core code five times and it 20% faster. never mind it still doesn't work right but man is it fast. And he works for lottery tickets."
- sufficient work ability, rarely an issue.
- teamwork - at work interface, negotiating, empathy with others. be relentlessly resourceful and useful, but get yours too.
- off-the-clock skills and interpersonal/appearance likability - a bunch of awkward single dudes can't say "no" to the socially-calibrated dude who goes out and convinces a bunch of attractive-enough females to hang-out with a bunch of random engineer dudes. be that guy, and you'll have friends bugging you all the time... turn your phone off and rock out to Spotify. :D