Startup founders in their 20s or early 30s won’t hire you if your more experienced than them (being older than them probably isn’t good either). Mature companies value experience (which comes with age).
Regardless of the details, there’s no such thing as “too old for X”, if there’s a well, there’s a way, as long as it’s within the reasonable limits, and even beyond that sometimes can be done.
You fail to mention whether you are a US citizen (or permanent resident) or not. This makes a huge difference. If you are a citizen, you can always rent for a year and find out yourself. There is no substitute for that.
I think the golden age of SV/Bay Area is behind us. It might come back with AI but I think this revolution will be more decentralized or happen somewhere else. That being said, that's irrelevant. A place (and a person) are complex and complicated things, and you can only make this call by trying the place for a few months.