I am beating a dead horse, but I can't emphasize this enough - be careful of your joints! You've only one body and it has to last. Weight training was fun when I was young, but it beats up the spine and the other joints unneccesarily. The same with high repetition calisthenics. It was a challenge and there are some conditioning benefits, but opportunity costs in the way of long term joint deterioration weigh out those benefits.

The bottom line is: as we age we lose the ability to recover and heal. That is a physiological fact that cannot be circumvented by nutrtition or exercise. We can stave it off, and I heartily recommend all do to the best of their abilities, but we are still going to age and eventually cash our chips in.

So what is the answer? The older I get, the more I believe tension exercise and moderate cardio-vascular exercise is the way to go. If you don't feel refreshed and invigorated after a workout, you've drained your vital forces - your endocrine system, by training too hard.