I think a big part of the "old people in the trenches" problem is that tech has historically had an "up or out" mentality. It seems like most of the older engineers I know either get pushed out or end up as principal engineers where they aren't routinely interacting with the younger people. I've encountered a few people who have managed to avoid this, but it's rare.

It doesn't help that our industry has been incredibly fast-moving compared to most industries, and our interview process is geared toward either being a fresh grad who's taken and algos class recently or knowing all the latest frameworks. Not a lot of places are interviewing on the sorts of experience you gain over a couple of decades in the industry -- which, to be fair, is often more intangible and harder to interview on.