I find the notion of age discrimination at 30+ to be simply ludicrous. I’ve been at multiple top tech companies, and the very common age ranges were mid-20s to (estimated) late-40s.

Older devs exist but they tend to be very senior with a lot of responsibility in my experience. Where does that leave the competent but non architect level dev who doesn't want to be responsible for that level of pressure? Maybe a 40 yr old wants to just take a mid level CRUD job for the purposes of keeping up with his mortgage and has no other ambitions beyond that? It seems like being "just a guy" is looked down upon the older you get which is not fair when there are plenty of those types of roles out there (mostly given to younger people)

Most HR and managers don't think someone who is 40 wants to work for entry-level / mid-level salaries intended for junior and early developers.

Is the 40 year old comfortable taking the same salary as an early/mid career dev? Therein lies the rub.

Yep, that’s it entirely. In your 20s it’s super easy to take a lot of risks, what do you have to lose?

When I was 20 I decided over coffee to move to the other side of the world. Had some savings, not a lot but just did it.

Now, at 37, there’s a mortgage to pay and a family to support.

I don’t have the runway to do two or three years of low pay again to switch to another field.

I am aggressive paying that down though, so that I have this option in my 40s.

You find it ludicrous because you haven't experienced it or seen it with your own eyes?

I think this phenomenon is hugely dependent on location.

I interviewed at a Fortune 100 tech company when I was 35. The head of the development center declared to me that "people don't come here to retire". I was hired because they needed a niche skill that I possessed.