Note that my original comment was not a comment about those that kept training and lost condition, but about those that stopped training or never started. The paper I linked clearly shows a downward trend and we all anecdotally feel the effects of age.

The universe doesn't care. If you do not use it, you will lose it. Age will get us all, but remember: what do we say to the god of death?

Have you seen the cross sections of muscle mass for people who kept training, even interrupted by injury, to the people who aged with sedentary lifestyles? It's night and day. Things get more difficult, but in an 80/20 sense the majority of frailty we associate with old age is the result of cessation of activity, rather than the cessation of activity being caused by the frailty of old age.

>involuntary loss of muscle mass and strength leading to sarcopenia and reduced physiological functions.

If you stop training or never start, your muscle loss is not involuntary.