At 37 I'm somewhere in the middle and I think there are two major factors at play in terms of SV age bias.
The first is a proliferation of young founders who have no experience and thus no frame of reference to evaluate older developers, so they just pattern match on the new tech they are familiar with. Nothing really to be done about that since convincing twentysomethings (particularly SV funded ones) of their hubris is a sisyphean task, and in any case it leaves talent on the table for those of us who actually know the value of a dollar.
The second, more troubling factor is founders who actually understand the value of experience, but prefer to take advantage of ambitious kids who are willing to work extreme hours for little equity and less salary. All else being equal, it's easier to find strong talent that isn't aware of (or bad at negotiating) their own value at a young age compared to when they get old and jaded.
As slimy as that is, I think it's a somewhat self-correcting problem in that good programmers are still too thin on the ground and startups who pass over old or minority candidates that are actually good will be at a competitive disadvantage. There is certainly a flood of young people going into technology via bootcamps or other means, but my experience so far is that there is a natural and unquantifiable talent component to being a good programmer which can not be solved by education. I firmly believe anyone can learn to program, but only a minority can ever learn to program well. At the moment, I interpret having learned to program before "startups" became a career move as a strong positive signal; chalk one up for the olds!