I've asked the same questions, I don't feel old but my bones creak when I get up to go for my two mile daily walk. I figure walking reminds the body to stay together after you hit the 50 year old mark. My grandma never stopped creating things, she was working on a quilt when she passed away at 93, the day before she left she was joking with the family drinking her daily bottle of beer.
I guess the saying 'Move it or lose it' hold's true at times. My Dad is in his 70's, enjoying mountain climbing and gigging with a brass band. Your grandma sounds like she had the right idea :)