I definitely don't currently intend to work at a large tech company. However, I live in Seattle (where there are a few), and most of the Ph.D. students I've had over the years do work at such companies, so I at least visit them regularly. Indeed, basically all people you see when you go to lunch there are way younger than me (I'm 45 years old).
Since CoCalc doesn't have any VC investment, and does have a solid and diverse base of customers, it's basically designed so that it is unlikely to fail unless I do something really risky. An example of something very risky would be raising venture capital or getting acquired -- we won't do that, since we have explicitly stated we won't to our customers and on our website, because some customers have been reluctant to consider using cocalc if we do take VC. In the worst case, CoCalc would be what some people call a "zombie startup" or "lifestyle business"... i.e., not growing much, and just marching on. However, I love working on CoCalc, and our customers love using it, so even that situation wouldn't be failure...
I'm 41 and work at Google, and I don't think age is a problem at all. As long as you don't expect to get better treatment because of your age, promotions will and salary will go to the best person not the older person.
FAANG in general are also pretty good about work-life balance which is good for us older people :-)
Since CoCalc doesn't have any VC investment, and does have a solid and diverse base of customers, it's basically designed so that it is unlikely to fail unless I do something really risky. An example of something very risky would be raising venture capital or getting acquired -- we won't do that, since we have explicitly stated we won't to our customers and on our website, because some customers have been reluctant to consider using cocalc if we do take VC. In the worst case, CoCalc would be what some people call a "zombie startup" or "lifestyle business"... i.e., not growing much, and just marching on. However, I love working on CoCalc, and our customers love using it, so even that situation wouldn't be failure...