I just bought a fat tire bike and tried it out yesterday at Griffin bike park in Terre Haute. The bike did fine on a flow trail and moved fast enough for me. If you're looking for something maybe a bit more leisurely they're worth a test ride. We're about the same age and as mentioned in other posts, I don't have plans to "send it!" for big air. I rode some "light trails" in Michigan on a commuter bike and it was quite enjoyable so figured the fat tire would work good also on trails which have some sand. I've visted Arizona the last couple years so could have used it then.Looking into it a bit I like the idea of the mountain bike and adjusting the tires if needed.
The Trek Marlin comes in this beautiful matte olive grey.... Seems affordable, relatively, haha.
It looks like a lot of the gravel bikes come with drop bars, and no suspension. Suspension sounds good.
The mountain bikes seem to be about 10 pounds heavier than a similar priced gravel bike.
Also, I just figured out what I am seeing in my neighborhood. The fat bikes, with the 4.5" knobby tires that sound like my truck tires when I don't rotate them enough!