I'm not a fan of backpacks, I prefer a cross body type shoulder bag/messenger bag. A stroller for the purpose you suggest would be impractical and more trouble than it is worth, IMO. Always needing to park it outside to enter ride queues, trying to make sure it stays dry, and the fact that something could get stolen, even in Disney.
As a senior myself, I'd recommend sharing a
scooter. If you are staying onsite, the busses accomodate them, and they are pretty reasonable to rent, and some companies will deliver to your resort amd leave it with bell services. (We've used
https://www.scooterbug.com/ with good results) You can put a small backpack in the basket and another full sized backpack on the floor board under your legs. When I travel with a friend of mine that has severe RA, we share a scooter, as sometimes he needs to walk a bit, but really needs the scooter most of the time. A manual wheelchair is also an option as you can hang the backpacks on the back. That's what my Mom and I did, as the walking was just to much for her after 3 hip surgeries. And yet another option would be not to carry so much stuff unless medically needed. My shoulder bag carries a lightweight jacket, a rain poncho, my phone, charging block, zipper cin purse type thing with my ID, medical insurance cards, Disney gift cards and a credit card, in case the room charge system is down, and sunscreen. With room for a few SMALL purchases in the parks.
The only times I've seen a stroller used as you suggest, there has always been a young child with the family.