70 here. No speed demon, never was. But I can still climb hills as good as many, better than some. One paved hill that I see riders on mtn bikes using the lowest gear to go up, I climbed in the middle ring on my LeMond road bike the other day (standing, but still, wasn't the granny gears). Think much depends on genes and how active you've stayed. I've always been on the slim side, couldn't gain weight if I wanted, and have always remained active. So, in my opinion, some of it is up to heredity, and some on how hard you work at it.