Back to the topic.
I am 58 and have been sailboarding for 29 years. Weigh about 72kg and 177cm tall. I would say pretty fit for my age. (Recently played a season of Water Polo for the local 3rd Grade Mens team). Swimming is pretty good too, but I prefer not to get into trouble, than have to swim in even though I have done this a couple of times. Funny thing is I have almost drowned on three separate occasions, two when sailing in waves and one when 7 months old in the bathtub. No bad lasting effects...I think...duh.
Slalom sailing is no problem A.T.M. I can go for a few hours and did 7 days in a row during summer this season. No major physical issues except for extra calluses on the hands. A small price to pay.
Freeride is also OK with no physical soreness afterward usually, but I do a few post sailing stretches given to me by a young female physio for the forearms and tendons.
Wave sailing however is a different story - if there are jumps involved then I have to be careful as I have had more injuries doing this than from any other form of sailing. The more jumps - the more soreness later on even if I land them, if I don't then it does hurt. If I end up doing wave riding with limited jumps, then the physicality of it is a lot less.
My dad had a heart attack at 55 even though he was an extremely fit man. He overdid it doing a 10km fun run during one summer and ended up with only 30% efficiency left in his heart when released from hospital. He did make it to 76 so I am reasonably confident I still have a few good years left in me.