The last pony we had (registered Shetland), lived to 32 years when he had to be put down due to advanced crippling arthritis. He never foundered but did colic quite easily, which we later found was due to the kids feeding him apples. Some ponies and many horses are very sensitive to apples.
32 is pretty average, my first horse died at 34 but she was put to sleep. 70? No way.