Training a thirteen year old horse?

I have a mare who used to be used for breeding. Other than breeding, people used to hop on her back and make her trot as fast as she could go around the farm. She did not understand cantering though. Now I bought the horse and have trained her to canter. I got her trot collected finally, but her canter is like galloping. I try circles, check and release and have tried to lunge her. Anyone know how to slow down my horse? And yes, I know it will take time.She may not have the strength to canter in a steady, non-galloping fashion.  This strength could be mental or physical.  My horse was a low-level hunter when I bought him and did not know Dressage (I do eventing).  His canter, though I could stop him, was fast and unbalanced when I asked him to carry himself like a Dressage horse.  He didn't have the strength in his mind to understand what I was asking (he's "fruity" sometimes) or the strength in his topline to do it even if he knew.

It's taken me a few months, but I built up his mental strength by doing Parelli Natural Horsemanship -- groundwork and in the saddle -- which made him more able to think through what I was asking, and I built up his physical strength doing gymnastics (bounces and 1-or-2-stride combinations), lots of stretching down and moving freely forward at the trot, trail riding a lot (though that did not necessarily help the muscles needed to maintain carriage, but it helped his baseline fitness).  Transitions help a lot too.  I just stayed patient and now he is quite good at cantering in a relaxed manner and maintaining that.  He could lighten his forehand more but that is what we are working on now.

As a picture, I rode a Dressage test with him before doing the above-mentioned exercises, and we got a 56 because he was stiff and hollow (don't know if you know this, but in eventing the lower scores are better, such as 20s and low 30s).  This year, his first time out after doing all these things, he was nervous and tense as he is inexperienced, but since he at least knew what I wanted, he could respond better and we got a 43.  Big difference!  Even if you don't like or want to do Dressage, the basics could help your mare.

Good luck!You need to do tons of balancing work at the canter. Circles, figure 8's, serpentines, ect. Anything that gets her bending and useing her body will help her balance. Do a lot of transitions. When she starts getting really fast at the canter, halt her, back her up, stand for a second, then ask for the canter agian. Lunging her at the canter will also help.Work your way up to a canter. Don't start out with the canter. Every day out go out and work with her  work our way up to the canter every day. Horses need at least 3 hours a day to be worked with. Get her comfortable and that way it will be much easier to work on her canter. Don't give up on that horses!keep up the good work.