I knew a guy in his early 80's who did a few of the local summits, class 3 at most. He used to do fifth way back when he was in his 50's, but wasn't a big climber at all. More old time MLC SC. He did the Muir Trail a couple times in his late 70's and early 80's, but I think now he's given it all up. Another guy I used to take along was in his 70's when he stopped peak bagging. Never says, "No" to a hike. Now it's, "We'll see (same thing)."
I'm hoping I have another 20 years, but seeing the mental debilitation, would almost rather be dead when you know MLC SC. Not a world I'd like, too mentally diminished for high tech.