SF and SV are very different places, in terms of the types of tech work available and what sorts of companies are hiring. I strongly get the sense from talking to people that the SF job market is much more biased towards startups, whereas SV is more of a combination of startups, huge companies like Cisco and Google, and everything in between. Also, I've got to think that there are vastly more jobs in SV to begin with, just based on population if nothing else.

So, someone living in SF and looking for work there would be much more likely to look around and think that the entire job market is driven by startups populated by a bunch of hubristic guys in their 20s who expect everyone to work 80+ hours a week and are more likely to be (at least subconsciously) ageist and more prone to being discriminatory in hiring people who they don't personally relate to (age/cultural/background differences, etc.).

I live in SV and have lots of friends who live in SF and commute to SV, or live in SF and decided to get into a startup because they were sick of the commute and wanted to do something different. I really get the sense that the only reason there is any tech job market at all in SF is because SV draws so much engineering talent, and there's a large population of younger engineers who want to live in SF so bad that they're basically willing an SF tech scene into existence by setting up startups there, so they don't have commute anymore.

Older engineers looking for work in SV are likely running into different problems. I see it all the time and am always paranoid that I'm falling into the exact same trap (I'm 42 BTW). You get a good job someplace. You continue working at that job for 5, 10, or 20 years. You become more and more valuable because you end up with really specialized knowledge, and carve out a really customized niche for yourself. Also, you get a raise every year. The end result is that after 10 years (or whatever), you're making a really good salary, and likely have very deep (but not so broad) knowledge about whatever your niche is.

Then, something bad happens (or you just get sick of whatever you were doing), so you go looking for a new job. Your great salary was from a combination of longevity, and very specialized knowledge of a particular code base. Unfortunately, when looking for a new job, you have neither of those things going for you. You can only hope for a decent starting salary, not an "I've been here for 10 years" salary, and it'll be hard or impossible to find a job where 100% of your deep, specialized knowledge carries right over into the new position. I think that for a lot of people the best case scenario is one where they're a good fit, but they've got to take a little pay cut because they're starting fresh in a new organization. They'll get back to where they were before, but they've got to work their way back there over the next 2-3 years.

None of this is anyone's fault, it's just the nature of the beast. The only defense against it is to always make an effort to keep your skills fresh, and not get sucked into a mode where you are 100% focused on learning what you need to know for your job and nothing else. A lot of people get comfortable and stop learning altogether, which might make things tough if they want to find a new job for similar pay. There's definitely something to be said for age and experience and maturity, and I think employers appreciate that as well, but not to the extent that they're going to totally ignore the technical requirements when hiring for a position.