Originally Posted by AnrewPL
Ridemoreworkless has a good point, a horse might be well into 5 or 6 before they start to settle down, and that’s about the age you should hold off the hard work to let them firm up physically too. But even after that age they might buck. The only one of my work horses I have left is Cisco, about 21 or22 now, the cranky old turd will throw one or two in, in really sneaky ways at that, to see if he can get you now and then. And the most unbelievable one I saw was an ancient racehorse us kids learned to ride on. He was so quiet we’d use him for a jungle gym and ride him into a waterhole and use him as a diving platform; the old guy stunned everyone when he threw someone once; any horse can buck. But by the sounds of it you have something a bit out of the average on your hands, get him re trained or get your money back.
I agree, there are many babies that are dead quiet, really nice horses, but sometime between I would say, about 3 and 6 years old, they will try some stuff and need to have a strong rider/handler to keep them developing well. It is all part of the growing process. A 3 or 4 year old may be really calm and have a great start, but they are technically still *babies* and only time and wet saddle blankets will make them truly "broke" in my definition.