I find it fascinating that when there is a discussion about age discrimination, most commenters have "advice" for the old farts how to stay current, learn current hip tech, be willing to work longer hours etc. However, we we talk about women in computing, it is always sexism and the discussion is about how the corporations need to change to attract more women. Pretty asymmetrical, don't you think?
I do think. Probably the same unconscious ageism in action: if you are having trouble getting hired and you're over 40, it's obviously because your skills are out of date. Hiring involves a lot of "People Like Us" evaluation, consciously in many cases. And if you're over 40, you're probably not like "Us" in SV.
My code is being used by probably a billion people right now (how many people are using windows?) How many people play on the playstation network? I'm currently working in a blockchain startup. Is that an out of date skill?
I don't mean for this to sound arrogant- as I said elsewhere wisdom and enthusiasm are very useful.
I think the correct mix for any engineering team I build is a range from junior, or even interns, to senior people.