Have you had anyone else ride him to see if he acts up with them, ie a more confident or more experienced rider might get a different ride. I also agree to rule out possible pain, chiro eval, vet eval. Is he up to date on teeth/floating,,,a bit hitting a sore tooth could cause 'behavior' issues which would be more evident at trot or canter than walk. Lots of layer of the onion to peel. To me, the buck and the reactiveness (heightened) are two separate issues that sometimes coincide,,,but who knows?
As to the spookiness and heightened behavior,,,imo this comes from innate personality AND from the situation,,in other words he may be naturally more reactive to things than say a super calm horse, but might be 'braver' and calmer with training. Sonny was very spooky when I got him, he got 'heightened' easily and didn't come down quickly. But after lots of groundwork with exposure to different environments (clinics, trail rides, trailering to different venues), he became less and less spooky and came down quicker if he did get upset. Also, there are things you can do to help him start thinking again Vs being reactive and emotional. I've been taught that a backing, sideways movement, or making the legs cross causes the horse to think instead of react, if that makes sense. Also, the first moment that I feel one is about to blow up, I probably would get off and do some groundwork. If getting off isnt an option, then I'd ask for back up, HQ yields, maybe sideways,,,stop and re-assess , rinse and repeat if necessary. It's rare that getting off really isnt an option. I've seen Sonny go from highly heightened to calm and blowing out after groundwork that had me standing with my back to a fence sending him in an arc to the left and right of me, with the fence giving him no choice but to change direction (yield of HQ-crossing of the feet), and he would be cantering like a maniac-head and tail high-throwing some bucks at the beginning,,calm, head below withers, blowing out after a bit.
I very much disagree with
ef that majority of us will stop riding in our fifties. I forgot to read that memo, and I have LOTS of friends who also missed it...LOL. I'm 69 and no thoughts of stopping riding. Again, I know LOTS of people riding who are over, some well over 50's.
One of my friends went thru over 10 horses because they all had behavior issues that scared her. After #10 she started taking horsemanship lessons (groundwork and riding) , built her confidence and gained techniques to work thru the problems and never got a #11. Oh, forgot to say that she still had all the horses, she just kept adding to her herd. Most folks couldn't do that! Only bringing up this example to say that it's so hard to get a perfect horse, the next one could seem calm and wonderful in the purchase process and turn out to be as 'bad' or worse. Just another thing to consider.
I lean toward possibly getting a trainer for him AND an instructor (not just riding,,,groundwork--I'd personlly recommend 'natural horsemanship-) for yourself. But, you have to go with your comfort levels and nothing at all wrong if you decide to sell him to someone who may be a better fit with him.
Stay safe. Have fun.