I'd say you never are. I rode up the lift a year I two ago with a guy that was I believe he said early 70's learning. He said he had been skiing since he was in his teens and just wanted to try something new! Lol
Mainly probably depends on how good of health the person is.
2011 Academy Propaganda Rev - 2012 Rome 390 Boss
2012 Never Summer SL 2012 - Ride Capo