Yeah the job growth is certainly a factor in why there are more younger devs, proportionally.

That said, it's still pretty rare for older devs to reach 25 years of experience while still writing code day-in, day-out for a company. Working a job just isn't how it goes these days.

There's research from Stack Overflow added to the post. There are also tons of comments here from developers who are older and run a consultancy or have moved up into management. That's what happens with many older developers.