Senior years?! 50 is the new 40. Here's a story to inspire you. My mother-in-law is 60-something (64?) and, in her adult life, gained a lot of weight (100 lb? 150 lb?) due to a medication she was on. She found a new, suitable substitute medication, and has shed nearly all of it. The woman is practically skinny. You're never too old to bring on a renaissance! You could say, oh, she had special circumstances. But it was still a lot of weight and it still took changing her eating habits to shed it.
It might take a year, but you can do it, and you'll see such a great improvement in your health and comfort - and appearance - after just 3 or 4 months. That's no time at all.
Now. About that shower curtain. You leave the decorative one out of the tub, right? You're talking about the liner, right? If you've had the *curtain* inside the tub, run it through the wash, according to the washing instructions, or take it to the dry cleaners, and consider it a lesson learned. That part stays out. As for the liner, *that* is what goes inside the tub. If you don't have a liner, I'd get a fabric one, because vinyl wreaks havoc with our health. And you can just throw a fabric one in the wash. Much less work.
Either way, here's the easiest daily regimen to keep from having to scrub a lot OR put it into the laundry:
Put vinegar into a good spray bottle (leave it in the shower so it's easy and you take no extra steps) and spray the liner, be it fabric or plastic, after every shower or two or so. You can keep a scrub brush (if fabric) or sponge (if vinyl) in the shower to help lift stuff off, if you want; I don't even (with a fabric liner, I've found, little care is required - I spray it once every couple of weeks - of course, I'm being a bit negligent, too). Then give it a quick rinse from the shower head. Voila!