Thank you guys for all your comments, they've been really helpful(: I'll be sure to tell Jack he has a few fans(;
APHAforlife: Haha he loves his food! He has been on Seminole Wellness Calm and Cool feed, but about a week ago he switched to a new food that I can't seem to remember the name of. I'll check next time I go out to see him(:
Bubba13: It's very possible he suffered from a shoulder injury, however it must have happened before he was found in the field. I don't have any records before his previous owner found him about a year ago. So all I can really say is that in the past year he has been completely sound and uninjured minus a few small cuts from being a bully in the field. I haven't had his back specifically examened, but the vet has checked him over a few times and hasn't found anything bothering him. If you think it would be beneficial, I'll certainly get him checked(: I'm only about 100 pounds, so luckily my weight isn't much for him at all.
Thanks again for all the feedback, I'm glad to know he doesn't have any terrible flaws, minus his "old boy" back. It is possible he's closer to 25 than 20, that was just the vets estimate, and of course she could have been wrong. I guess for all intensive purposes I'll call him a Thoroughbred or Appendix, since that's definitely what everyone has pointed to. We all thought Thoroughbred too, but I always like to get other opinions. I sure wish I'd gotten him when he was younger, I'd love to have pictures to show you guys of him when he was young and dashing!
As for comments about how he rides, his canter is to die for. It's like floating on a cloud. His trot, however, is pretty bumpy, but it's easy to post to!(;