The oldest pony "sugarpuff" has died at the age of.....get this....56 years old. The oldest I have ever seen was a 44 year old pony when I was working in Ocala Fl. I was always told there were 2 kinds of ponies, those that had foundered and those that were going to. That old one had foundered at 20 and was on 1 gram of bute daily for 24 years.
(Sugar Puff, a 10hh Shetland-Exmoor gelding was put down at home in West Sussex on 25 May following "complicated problems" with his health.
Owner Sally Botting told H&H: "His organs packed up. He had been fine in the morning but then just collapsed. The vet said no more could be done.")
There was a report several years ago of a Florida cracker-horse that was 55, it was a search done by Purina for their Equine Senior diet. Either way it shows that horses and ponies can live a really long time if you keep up with good health management.