Use it or lose it. Aging affects everyone until the end. But the effects most certainly can be mitigated and quality of life made better than it otherwise would be.

I've watched acquaintenaces and family members say, either aloud or by their actions, "I'm old now." They basically quit learning, quit striving to improve, quit trying new things. They sat down and waited for God. Not surprisingly, their later years were not quality ones...certainly not as good as they could have been. Be careful when describing the physical effects and expectations of aging...many of the ill effects derive not so much from aging but from inactivity (physical and mental). And/or some other choice; e.g., smoking, obesity, substance abuse, etc.

To paraphrase George Burns, "There's nothing I can't do at 90 that I could do at 18. Which shows how pitiful I was at 18." :D In my senior years I find I'm stronger and in better shape then as a young adult because I exercise and gave up smoking long ago. My fret hand strength and flexibility is much greater because I practice more. IMO, most could say the same if they wanted it enough to take the proper actions.

Yup, aging grabs us all. But we have some control over how long we get to go and a lot of control over how good that journey is going to be. It's no surprise to me to find lots of really old musicians stil playing. As for guitar, until I can't play or quit "I'm never going to be as bad as I am today."