I have found the western horses style riding groups are very concerned about adults riding something shorter than 14 hands, some go to 14.2.One of the ring stewards at the meeting that I asked for a rule change to allow adults on ponies said"I will be sick if I see some 6'person setting on some 500lb pony and competing. I said, "it ain't gonna happen because they can't move well enough under saddle if the mass on the saddle is that heavy." She told me someone will try it and I told her I have seen the equivalent with a 300+lb man on a narrow built and rather petite thoroughbred at the show and she bucked him off before he got near the poles, and I have to say, he got what he deserved. So size doesn't stop people from making bad decisions on what they will try to ride, just hope they learn from their bad decisions and make better choiced mounts the next time they go for a ride in the speed ring. I have my kids competing at Maryland Western Horsemens Association and they have been kickin butt for many years at the kid level but now my 15 year old is against the adults and his mount can't do better than 2nd or 3rd in the speed events. I am sure he would be better if my son worked the events in practice at home but he rides for fun, not that serious and just goes for rides with anyone that wants to go faaaassssttttt. Otherwise, he would rather forget it. Good thing the gelding he likes is mostly in the same frame of mind as him and wants to go, very competive ride.Jeannette