You're acting like this is some new development (presumably because you just now learned about it), but it's been this way since forever. If it were legally dodgy, then why hasn't it been challenged in court and torn apart? Because you're the first to be offended by it, or because it isn't dodgy and the FAA are on firm ground? The latter. Age limits for pilots and ATC are textbook examples of BFOQs.

> This isn’t something that we just take their word for it.

If you want to hit the books, knock yourself out. I am perfectly content to take the FAA's word for it, and think you'd be wasting your time.