I generally don't even get on my horses til their at least 3 yrs old because I'm worried for their joints although I don't work them hard at all. I rarely bring them to a trot when I first start riding. What do you guys think? The Breeds I'd be riding is a APHA filly, she's about 14.2-.3 hhs right now. And the other filly is an app x arab cross about 14.1-.2hhs. The paint is medium built while the app is fairly stocky. I wouldnt be trotting them at all but just to walk around to get them used to it. What do you think?