Join Date: Oct 2009
Location: Just south of sanity
At his age and with no physical limitations? Yes, it's bad. What happens if you can no longer keep your animals? Where do you think an untrained adult horse is going to end up?
Send him to a local trainer, where you can keep tabs on him. Any trainer worth the money is going to encourage you to come out and watch, not try to keep you away.
As far as the cost of training? Yes, it's expensive. But if you want your horse to have the best chance at a good, useful life, then training is the way to go.