"Aging gracefully" = knowing how far you can push your limits without killing yourself. Something occurred years ago, in my late 50s, on a canoe trip in the BWCAW: my older son was healthier and in great physical shape, bigger and stronger than I. Even though he was a long distance runner, worked out constantly, I had more effective endurance than he did. I'd learned to pace myself, he had not, yet. we teased him by calling him "Evenrude"—flat out until he was out of gas. Learning how to use your body's "throttle" intelligently apparently only comes with experience and age.