Use as much sarcasm as you like...
It's cheap and there's plenty of it around.
There are many sides to this argument but the two that really matter, in my opinion, are safety and the politics of the workplace.
There's never been a convincing safety argument for a hard age limit, given how variable each person's physical condition is, how to balance the negatives of increasing age against the positives of increasing experience... All in all, after much back-and-forth the USA just lifted the Age 60 Ban on airline pilots and that says a lot.
The politics of the workplace is against aged pilots, of course! Well, from the self-interested perspective of a young pilot the crocks should all be dragged out of that left seat kicking and screaming and never mind the state of their retirement funds or whatever. This has nothing to do with safety per se but one can easily use a safety-related argument to pursue this end.
There have been relatively few crashes due to a pilot dying or becoming incapacitated at the controls. (Google: Reed Pigman for one in particular, though.) How many are due to inexperience, though? Some I read about, I have to think, "Gee, I really think I have learned not to do THAT!"
The grumpy elders end up in the circle of wagons with the wild, half-naked yoof out there riding around in circles wearing their warpaint and screaming. So? Not a lot of learning goes on in these dialogues.