I've seen that in action. An older dev was an absolute burden on a hack day moving at a snail's pace. But for long term architecture he always had super valuable "oh I didn't think of that" things to say.

He was so awesome to have on the team, at the cost of sometimes having to watch him crawl toward a few lines of code. Not a hard choice in my opinion.

Of course I've seen the whole spectrum. Useless old people. Useless young people. It's best to simply be a meritocracy.