A pony can live to age 70? That is absolutely not true. That said, you are correct on the founder issue, nearly all ponies will founder at some point.
I have known ponies that old. Course these are small ponies.
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.