I'm 64, been mt. and road cycling since I was 33. I still mt. bike, mostly in fall thru spring when the temps drop round these part. The trail riding is terrific in fall/winter even when the ground is frozen.
I know my wife questions the mt. biking, especially as I took a hard fall a week or so ago on a really nice single track. Didn't see a stump under the leaves, then caught the h-bar on a tree and was ejected onto the ground. I was moving at a clip as well. Badly bruised lower ribs (maybe cracked, but no difference), bad bruise on inner thigh with a black and blue going from mid calf to mid thigh. I was in LOT of pain last week, getting better this week and will try some easy trail stuff this weekend.
Thing is, it's hard to recognize that my age is a limit, especially when I'm able to handle the not too technical stuff like I have all my life. Getting hurt just takes forever to heal, so I try not to fall. And I DO NOT ride anything technical or in the least bit sketchy, especially when I'm alone. A riding buddy who's 8 years younger, fell a few years back on a solo mt. bike ride, broke 2 vertebrae in his neck. He was able to call 911, it took them 45 minutes to find him, he's lucky it wasn't super cold, he might have died of hypothermia. They had to helicopter him out. I'm unclear how he's able to convince his wife that he's OK to solo, except that he too has been doing this all his life so how to stop now ?.