Dave: I'm guessing we are about the same age, and I've noticed my body changing this past year, something I really did not expect for another ten years or so.
I don't work as long on wood as I have in the past, so I do it more often. If I'm sore one day, I'll push myself out the door for an hour, and more often than not work through it, feeling better with exercise. It may mean just doing clean up for the next cutting session. Regardless, the dogs love the wood lot. I noodle much more frequently than in the past, figuring down time from a strain isn't worth the risk.
I have copd, which has been acting up, and I attribute it to fine airborne dust when cutting and splitting as I do on a log bench. This past week I've worn a full face 3M mask when cutting. It is a negative pressure mask, and not ideal with a beard, but it is sealing and working.
As for your situation, jrider makes some very good points about seasoned wood producing more heat and a cleaner burn.
We burn scraps and uglies in a wood stove after they have been split down and bundled on a pallet for a year. It takes time to process a punky log and throw it in the junk bin, to rehandle and bundle later, but that's how we deal with scrap. I think there is four cord, 16 pallets of it from last year, to brunches year. Not very efficient but I'm not going to push it over the bank and create a mess in the woods either.
Important to be a good steward of your body and your land, and that may take some additional effort, and changes with age.
Deliveries for me have been enjoyable in that I hand unload off a flatbed. The enjoyable part is talking with customers while unloading. The reality is that it takes too long; there is a lot of climbing around to strap the load, to uncover and unload; and often standing on the edges while working. So, I've ordered a dump trailer, which will be a huge change for me next season. Mostly because of this topic, age.
Do what you have to do, just keep enjoying it.