I'm so sorry you're in such a fix. I will tell you, over the years I've learned to get 2nd, 3rd and even 4th opinions. Call one of the big show barns and ask for a vet and farrier referral. Local vets who are not equine practitioners can seldom tell one end of the horse from another - hence the huge span of age remarks. Call a well respected *certified* farrier to check your horse's feet. It may cost a few more dollars but having a horse is a sacrifice and one that should be yours, not the horse's.
Lastly, a dressage horse does not a jumper make. Normally, if their is an especially talented jumper, he may also be retrained as a lower level dressage horse. Dressage is not an instant success thing but requires years and years of dedication. A horse that is already 12 does not have the time or strength left to make it to FEI.
I wish you well and hope you are willing to give your fellow a fair shake.
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