Within the vast range of the animal kingdom, there are many examples of metabolic processes more resilient and long-lasting than even exceptional mammals such as we humans. Whales, for example, appear to be capable of a century or two. Large tortoises are good for that sort of run as well.
On that note, the New York Times mentioned turtle longevity in passing today:
Dr. Christopher J. Raxworthy, the associate curator of herpetology at the American Museum of Natural History, says the liver, lungs and kidneys of a centenarian turtle are virtually indistinguishable from those of its teenage counterpart, a Ponce de Leonic quality that has inspired investigators to begin examining the turtle genome for novel longevity genes.
“Turtles don’t really die of old age,” Dr. Raxworthy said. In fact, if turtles didn’t get eaten, crushed by an automobile or fall prey to a disease, he said, they might just live indefinitely.
While I'm not sure that manipulating our human metabolisms for greater longevity is the best path forward at this time, I point this out as a reminder that the realm of the possible is much larger than most people credit - in the long term, armed with future biotechnology, at least. Scientists have learned a great deal about the biochemistry and genetics of longevity from yeast, flies and mice in past decades; there is no reason we can't also learn from far older animals.