Shingashina said:

If he's a really quiet, gentle horse, just try walking with him. You can get a feel for how he moves and get comfortable with him. When I was 3, my mom put me on a 16.2 hh TB mare with a halter and rope and turned me loose. My mom used to be a trainer and had trained that mare herself, so she knew what the horse was like. This was a horse that I petted and led around all the time. This horse would not turn, stop, or go faster unless you asked. She was more than happy to walk wherever I wanted in the pasture, stop, and stand there for a while. I was tiny and the horse was huge, but she had a lot of training and a gentle attitude behind her. All I knew was to steer, stop, and go forward. All I ever did with that horse was walk around, and I moved up to trotting with a 15.2 hh QH mare. I just took things slow and never got scared. I rode bareback for years before I started using a saddle, and because of that, I have a great seat. If his height is scary, just hang out with him for a while and see what a sweet, gentle thing the horse can be. That always helps.