Here is a picture of Cowboy, who is 13 hands, with my 5' daughter-in-law on him:
Here is another picture of him, taken before the one above. It was his first day with us, and we didn't appreciate how afraid he was in his new home. He had galloped a dozen laps with my DIL and she ended up turning him into the fence and hopping off when he stopped for the fence...so I rode him. At the time the picture was taken, he had galloped a dozen laps before I asked him to slow, and had then done a couple more with this level of pressure on the reins. He stopped a short distance later and started to figure out stopping worked better if you did it in a more timely manner...so he started to calm down. That was when my DIL got back on him. So yes, the picture looks awful, but it is the only one with me (5'8", 175-180 lbs) on him:
You can see Cowboy is short but stocky. His shoulders are narrow but his back is short & broad. His legs are thick and have a lot of bone. I'd guess his weight at around 700, so with saddle, I'm at 30% of his body weight. He DOES need to adjust his stride for my weight, but he seems quite content to canter or gallop with me on him. I have to adjust my weight in the turns because of his short "wheelbase". He now has an Abetta saddle that fits him much better than the saddle in the picture.
I see no sign that he is harmed by my riding him. But I really am at the upper limit of weight, because he has to adjust so much to carry me. Height is not an issue. I like
riding a 'low to the ground' model! My 5'2" wife rides him, and appreciates that he cannot outmuscle her as easily. She doesn't ride a lot, and she also likes being lower to the ground.
Here is a good article on weight & horses: How Much Weight Can Your Horse Safely Carry?
When I have more time, I want to try riding Cowboy on a regular basis. I think he will be a good horse for riding. He is sure-footed and was born wild in the desert. But he also has good conformation for carrying higher weights...