Don't even worry about it....put it off as long as you reasonably can. You don't have to find "when to swallow the anchor". That time will find you. Fretting about it just messes up the time that you have remaining. And for each one of us, that will be different. I'm 72, have a Catalina 320, single hand it, and don't plan to give it up anytime soon. What you did or should have done in the past is gone. You have only now and the future....if there is something you want to do or keeping doing, go for it...the opportunity will never be greater than now. You will have to give some consideration to the realities of getting older, but usually these are just treaking the plan a bit. Like some of the others, I get the boat yard to do bottom, diver to occasionally clean bottom. I've had four sailboats, Venture 24, Catalina 22, Kells 28, and Catalina 320. The 320 is the easiest of all to sail, has lots of room, is steady moving about the wide decks. Since I hire the heavy maintenance, cleaning the boat is the hardest thing. I don't take long trips nor do I try to sail in high winds. I love the boat and often just walk down to the dock and admire it or sit on it or take it out....whatever suits my fancy. I wear a pouch type inflatable life jacket, and have recently began to use a harness and tether.
As for taking up new things, my wife and I just bought a beach cottage at the ocean. I plan to do more fishing with my 19' motor boat and spend time on the beach. The cottage was owned by a 84 year old who went swimming everyday. (Not giving up the sailboat either).
When I sold the Venture, it was to a man 68 years old who was just taking up sailing. I saw him on the water for probably another 5 yrs. and then lost track.
At a previous marina, there were two brothers who sailed a Northwind 29. They were probably in their mid 80's before I lost track of them.
So don't fret, make some adjustments, and "keep on keeping on".