About ten years ago, when I was in my mid-thirties, a friend and I hiked up to Big Pine Lake #1 in the Eastern Sierra. This was before I went lightweight, and the two of us just about died making it up, lugging 50 pound packs (out of shape, knee problems, general whining). On the way back down two days later, dragging along and whining all the way, this guy passes us up like we were standing still (come to think of it, maybe we were standing still). He had a spring in his step, and looked fresh as a daisy.

When we finally got back to the trailhead, he was still there, and we struck up a conversation. He had hiked all the way to Big Pine Lake # 8, several miles further than we'd gone. Turned out he had just celebrated his 69th birthday. That guy became my role model, and at that point I resolved to still be backpacking at 70.
It's great to hear that so many of you "youngsters" are still going strong -- gives me renewed hope.