I am mentally young but some of my joints are 100 years old according to my doctor. Of course some of my joints and other enhancements are only a couple of years old.
When I was 46, my doctor said I had the hip joints of a 75 year old. Thank God for replacement joints.
It's funny how that aging thing works. My dad is 77, took reasonably good care of himself throughout his life, and kept active. Last 3 years have been pretty down hill though. He and his wife just moved out of their house into senior housing. He's got something kind of like Parkinson's that apparently isn't and had to give up woodworking, daily walks, the accordion, and a lot of his other favorite things. Hard to watch the decline, but he has had many good years.
My mother on the other hand, is 8 days younger and just got back from a three week trip to Israel and Jordan with a six mile walk in and out of Petra. She finally decided to retire last year, but ended up working part time instead. She is in great shape and doesn't even have any grey hair. Go figure. For whatever reason, that side of the family ages slower than normal people; they all look and act 10-20 years younger than their actual age. Glad I take after that side I'd hate to have to act my real age!