I'm 57 and just started skiing four years ago. Wish I had found the sport twenty+ years ago when I was much more athletic. Last seven years have been focused on being single dad and lost some of my fitness being mainly chauffeur, cook and fan at son's sports events. Now that son is a HS senior and no longer in organized sports, I should have more time to get in shape, but it is hard to get motivated until a couple months before ski season. I have a leg workout I followed last year which kept me from having cooked legs by afternoons ski days and have started it again for this coming season.
I'm a high intermediate trying to advance so will be doing some black runs and practicing on bumps to get there this season. Working in a non-ski part of the country makes it challenging and more expensive, but still plan on getting ~25 ski days in 2015-16 on my RMP Super Pass+. Longer term goal is to be skiing double-blacks before I turn 60 since I expect that my reflexes and flexibility will diminish in my 60's (they have already somewhat) to the point where skiing double blacks would be ill advised.
I turn 60 next year. In way better shape than 5 years ago. Mostly because I had to rehab a knee, wanted to increase the fun I have skiing instead of coasting. Invested in a gym membership, a personal trainer, and high level lessons. Used to think 60 would be the end of improvement, but now know that if I keep working on ski conditioning and general fitness during the off season than no reason I can't be a better skier 5-10 years from now. There used to be places at Alta that I would look at from a lift or along a traverse and say "no way" but now I think "hmm, that looks like fun in the right snow conditions."
Did you see the reference to the book Younger Next Year?