This is the best light you can shine on the discrimination. Most often it really is managers taking their “seniority” literally. As in, they don’t want to take the risk their reports are smarter, more experienced or capable of replacing them, so they discriminate on the basis of age. It’s counterintuitive, but this feels truest from my historical observation.
Big organizations have done better, and maybe the view is a bit stale and who knows.
If you take age out of the equation, is there supposed to be something wrong with preferring to hire people who are willing to work longer for less pay over people who aren't willing to work as long who want more pay?
And I also generally believe it's bad, because it breeds a toxic and self-eating culture.