I'm in the age is a number camp; I think the mind and the body are the telling factors. I'm 62 and don't feel old (although people tell me that I am).
I have been very fortunate; despite having a few knee clean outs and shoulder jobs done though a long Army career jumping and carrying heavy shit long distances I am in pretty good shape. I think there are more mental scars to deal with than physical ones.
Playing Rugby during the week and League on weekends until I was 42 and then transitioning to touch footy has kept my mobile. I'm still playing touch in the local competiton. It is small country town so it is no big deal, there are some serious teams but I play with a mix of current and ex local rugby players. A couple in their mid 50s, most just retired from playing and a few still playing with the youngest being 18. It is great to be able to mix with such a divers crown socially as much as playing as there are farmers, teachers, stock agents and tradies in the team all with different expereinces and conversations to have over a beer. I think that is what really "keeps you young"; the mind and the environment you put yourself in. Hang with old people you will feel old!
I went to the St Marys Old Boys day a few weeks ago. Compared to most there I was in pretty good shape and there were many worn bodies carrying too much weight, now sitting in the chais their old man sat in when I was a kid. Which was the reason I left and joined the Army at 17 - I didn't want to be sitting in those chairs when I am where I am now. Still a few very fit buggers though. While it was great o catch up and kick on until well in the morning (so the piss fitness is still OK) most had grown into old because they followed their old mans footsteps, played, hung around with the same crowd, socialise together, on the punt together and old together.
Am I slower and find things a little harder, sure, but I really think as long as you keep moving a doing things you don't ned to stop until the body tells you to.
My lovely wife keeps telling me I'm getting too oldfor the shit I do. She may be right but I will slow down when I feel it is time. I'm sure that day is not too far off - but I want to push it as far out as possible. I expect that it is the old adage of use it or lose it is true. I know I am fortunate both health and body wise and I am greatful for that.
I am heading out to do some shuttle runs in a self imposed pre season for touch (starts in a month). Anyone want to join me?