I think the most important change that I have noticed is the desire to win or give it everything you have.
When I was younger I was very competitive with myself and with others. It did not make any difference what it was, tennis, chess, research grants or just about anything else. Giving it everything you've got made life good, enjoyable and often rewarding. I was not a pool player back then. Now the quality of the game and who I am playing with matters much more than winning. If the other guy needs to win that badly, I simply don't care. I know who I am and what I can do. Now I usually play for two hours by myself for every hour I play with someone else. It just isn't about winning any more.
At my age (69) I am in pretty good shape, my stamina is about as good as ever, eye sight is actually better with cataract surgery, and I know I am as tenacious as ever as I just finished a one year complete overhaul of the house we purchased here in Florida. I gutted it, with new sub flooring, all new wall studs, ceiling rafters, all new plumbing, electrical wiring, and of course all the plaster board and finishing along with new bathrooms and a completely new kitchen. And I did every last thing myself with no help from any one except a few days here and there when friends stopped in. So ya see it is not about the physical or mental aspects as we age it is about a change in priorities. I have played for 25 years now and I love it, but on my terms and with the people I like to play with.
To every season there is a reason, turn, turn, turn.
And while it may be difficult for some of the younger ones to understand, I am having the best time of my life right now. There is no longer any reason to be anything other than who I choose to be. I never realized how driven I was by my society and the needs of others until I got here. Keep your health and look forward to getting older, it can be the best of times --- truly.