I recently downsized (somewhat). Didn't go all the way from 3/4 ton to 1/2 ton. Went from F250 short bed crewcab, to a Nissan Titan XD (XD version is bigger than standard size Titan). Both with gas engines. The Nissan is a little bit smaller than the Super Duty, with slightly less tow capacity and payload. I gained a little maneuverability, better performance, 5 - 6 MPG, and still have capacity to tow my 8000 lb travel trailer. Also gained in
towing capability, in that the Titan came with factory prep for gooseneck hitch. I'm now set up (with added accessories) to tow bumper pull, gooseneck, or fifth wheel. I don't tow often so, the biggest benefit is the jump from 12 to 18 MPG.
I too, was considering my age and the age of the F250. I'm 64 and the F250 was 11 years old. I figured, if my new truck lasted 11 years, I would be 75, and probably won't be interested in dragging that trailer around.