I'll be 69 around Christmas and still mtn.biking on my heavy arsed steel GT. Still riding roots, rocks, stream crossings, mild drops, nothing like the younger generation on dual-susp, but not too awfully tame either. I do find there are sections now tho, that I'll think twice about, maybe even walk, that I used to ride. But I'm still riding and hope to be able to continue for a good long while! Oh, and because I still ride some "iffy" trails, I don't go out there alone.