It is more a question of attitude and health than it is age. I am a 63 YO male and I am still quite active. If she wants it she should be getting it. Pussy is a terrible thing to waste. Sex is a great cardio workout, I haven't found any workout that is more fun. Getting her toes curled will help keep her young. It probably would be a good idea to check with her doctor and make sure there aren't any health concerns and she probably should start out at a moderate pace. No all nighters, at least not at first.