FWIW, the most common functional, day to day problems of the elderly involve frailty, which decomposes into muscle atrophy (typically more upper body) and balance problems (typically more lower body). Both exacerbated by OA. Recent reports that a good predictor of terminal decline is walking stride length and speed. Women are affected more than men; you guys may live longer but IME a depressing amount of that can be in a chair or using a walker.
Anyway, I think skiing may preselect folks at any point past early middle age who have managed to retain balance and strength. Can it make us stay that way? Debatable. I think more of an effect than a cause, although an active lifestyle that includes skiing probably also includes a lot of other stuff that keeps the muscle mass up and the balance there. (Which according to a ballerina I knew is also mostly about muscle strength.)
But OP question: As long as I can. But not going to ski when my lean mass and balance are asking for a broken hip that will put me down for good. I hope that 100 year old has real good bone density...
Go hit that gym/bike/trail/pool guys.