I don't work anywhere near silicon valley but I am in a very small (<10 people) dev shop on the east coast and my experience has actually been exactly opposite.

I don't work anywhere near silicon valley but I am in a very small (<10 people) dev shop on the east coast and my experience has actually been exactly opposite. Out of the 4 developers I am currently the youngest at 32 (we had a 23 y/o at one point though for a period of time). The IT/dev industry here seems to be older on average with lots of devs in the 40-50 range. I have noticed some minor ageism towards younger developers but it tends to be more jovial teasing and joking about how lucky younger devs are to have the tech ecosystems that we do as opposed to 10-20 years ago. Most of the ageism I see is related to popular culture (music, movies, etc) which can still be somewhat toxic when any age group assumes that only the media from their generation was good and everything else is crap. I have noticed more bias against devs without formal education (which everyone else has with either bachelors or masters in CS) but if a well self-taught dev without a degree came in I don't think it would be an issue. For the most part though the "older" (its hard to think of people in their early-mid 40's as old right now) devs have a wealth of experience from whom I parasitically absorb as much as I can. It doesn't hurt that they are as competent in new tech stacks as most younger devs (even if they are more conservative about when to adopt new tools, giving them time to mature). The culture here is that someone has to make a really good case for why we should pull a ton of overtime, more often than not someone made promises they shouldn't have and its not our job to deliver on timeframes we were not consulted on. What OT work I have done I have been compensated extra for but it is partly the influence of the older devs that makes me feel like I should expect compensation when I go above and beyond. Thats not to say I'm not willing to do it to help the company (which helps us all), but I think I was able to pass the naive stage a lot quicker and I could have been taken advantage of much more in a bigger company without our developer culture.