I was just about your age when I got my OTTB with the same issues on trails.
I had a smallish group of friends who trailrode & I’d end up riding to the trailhead with them, then when he’d start his Post Parade jigging, turn around and head back to the arena for some work.
Happily there was a large unfenced field between the trails & the barn.
So once he got the idea that acting like it was Post Time meant back to work indoors, we progressed to riding alone in the field.
There was also another rider with a bombproof horse who’d go out with just me & my TB.
That helped as when my guy spooked, the other horse was “Meh” so the spooking decreased.
It took time, and for years every Spring was a repeat: Jig, Spook & finally relax - until finally I could ride him on the buckle, alone or with others.
Good advice on here already - especially from McGurk :yes: