Iron hors - hey! You're just a young buck!
Read this article about Sir Francis Chichester in wikipedia. Also note, besides sailing solo around the world, he tried to sail 4,000 miles in 20 days and missed by one day. That means he'd have to AVERAGE 200 miles per day! This may not mean much to someone more or less just getting started, relatively speaking, but that is an accomplishment. And.... at age 69!
http://en.wikipedia.org/wiki/Francis_Chichester
My dad had boats all his life but was basically a powerboater. His first boat was a sailboat, for a couple years, and then all power boats until he was in his 80s and then he got another sailboat. Finally sold it shortly before he was 90.
If I could make some suggestions it would be to try to stay limber and not let those mussels get unused. Boating, and especially sailing, can be reactive because you're on a moving deck, or things happen fast, and you try to react by pulling, pushing, lifting, turning, etc. and those mussels just aren't as limber as they used to be.
Also, try to protect yourself from the wind and sun. The sun can cause eye problems, I think cataracts? or whatever. Also skin cancer could be a problem. Otherwise, it's good exercise.
The good part about being older is you're more mature so you'll hopefully avoid taking risks that you shouldn't.
Oh, and that brings up another thought: If you have any teenage grandkids, try to get them out sailing while they still know everything!