Living and working in the Boston tech market, I have a lot of thoughts about Ageism. It's very much alive and well here. There's also a severe case of Elitism if you didn't go to MIT or Harvard, too. I'd like to think more about this and write dome some elegant thoughts, but...
I'll sum it up as it's a little humbling but massively humiliating. It's extremely frustrated being interviewed by people with obviously way less experience and people applying their hiring "playbook" without much thought. I'm pretty sure many companies hiring is explicitly catered to aging people out, or at least setting a different bar for older engineers.
Also, when I do get a job offer it's for quite a bit lower salary that much younger, less experienced people who are two or three years out of school are making in this market. It's almost as if the tech industry wants most of the people to have two or three years experience.
I've been equating it to working in Hollywood to some.
Still trying to figure out where I went wrong in my career, but as others have said below, not all startups you work for succeed, not all companies you create succeed, lock-up periods, senior executive corruption (I worked for a publicly traded company where the CFO actually went to jail), etc.