I LOVE older horses! My two geldings are 20 and 24, and they're they best. There is a lady that boards her horse at our barn, he's 31, and she still rides him. Not just walking either, that guy can GO! My 24 yo is still in great health, and a blast to ride. I think getting an older horse is an awesome idea, he just may require a few supplements and some extra care. Also, keep an eye on his teeth and make sure they stay as healthy as possible.