The best marksman I've ever known was my late grandfather, who was at first turned down for military service because his trigger finger was handicapped (it could hardly wiggle). He ended up a Lt. Col. in the Air Force regardless, and was very much qualified in pistol marksmanship. Even in his 60's he outdid everybody in the turkey shoots, using his middle finger to squeeze the trigger. My dad would be not far behind with his second place ham. And some say old people's eyesight is bad!
There's the familiar phrase, "You can't teach an old dog new tricks." That's a crock of poo. You're never too old to start working out unless you medically can't. (I've decided I'm going to buy my first motorcycle when I'm 70 and tote my great-grandkids around in the sidecar.)