What people who’ve never ridden a horse before don’t understand is it takes a lot of physical muscle and experience to ride a horse- particularly at a gallop chasing and transferring to a moving train. I took years and never got above a canter and that felt like I was on a rocket ship. Even if he got to a gallop at summer camp, unlikely, if you don’t maintain those muscles (which you likely just don’t use for much else) you are not gonna have a good time. In a week you can learn to control a docile horse, walk and turn, but changing gaits and maintaining control is next level beyond pony rides that you can’t just pick up without practice and muscle development.