'Define Old'
Hard thing to do but what's needed is an 'age' and that's it, everyone goes.
62, 65 whatever. Fly 'til you die IMO is unacceptable. There's an old boy network going as well. It's hard to fail someone you've known for years, but Sim instructors, Check Pilots, Line guys, find it pretty hard to do the deed and all the associated paperwork and nasty meetings, better to leave it to someone else.