Do you have a citation for this? Specifically, "after your late 60s": are you talking about people who don't squat ever, and then try to in their late 60s? Or

Do you have a citation for this? Specifically, "after your late 60s": are you talking about people who don't squat ever, and then try to in their late 60s? Or are you talking about people who squat regularly and find themselves unable to squat after 60? If the latter, I find it hard to believe but I am open to citations.