You'd have to start it at 50 or so, cause I've come across some who at 55 couldn't hold a flame to some 65 yr olds cognitively, and probably never could.

It's kind of like driving, and if anyone here has old enough parents, you get the "fun" opportunity of telling ma/pa that (after your visit and noticing that three corners of their car has scrapes on it), it's probably time to leave the driving to someone else. No one wants to admit/nor can they likely see it, when they haven't retained the cognitive powers of the past.