Aches and pains after doing a tiny bit of exercise is expected in the elderly.

You could try a Bodypump class between sessions or do the same thign at home with a simple 10kg bar with 5 kg on either end.
Squats - start with 10, then 20, then 30, then 40, then 50, on the sam,e weight. That's 150 reps. Expect to take a few weeks to build up to taht. SAiling will not hurt you after that.
Add some upright rows, and some military press. Use a similar set progression, staying on the same weight the whole time. If you have a bench, add bench press at the same weight, lots of reps.
Total cost will be less than a mast extension tube.

You can vary that with power-cleans, which a lift from the bar at your knees to above your head in one smooth movement, with maybe a little break as your hands come past your shoulders.
Legs, lower back, abs, hands, chest and arms all in one go.

Also, see what happens when you are planing and you completely let go of your rig. It should sit there for a few secs before slowly drifting off course. If not, you need to adjust something. You can then start sailing with one finger on teh rig.
If you are getting too knackered, you are either under or over powered too. Dropping lots of turns is hard work too, but it sounds like you are really working on that. If you are powered nicely on a well balanced rig, you will make more turns and get less tired.