This worm is in a Greek myth, and not the fun Greek myth where people get knocked up by rain. It's in a depressing, ironic Greek myth that instructs people not to reach for the power of the gods.
Ever heard of Tithonus? His story is one of the less popular Greek myths, and once you've heard it, you'll realize why it was so unpopular. Tithonus was a prince of Troy. He slept with his window open, so the earliest rays of light woke him from sleep. Aurora, the goddess of the dawn, looked in on him every morning, and was so taken with his beauty and his voice that she fell in love. She took him to Zeus, the king of the gods, and begged tearfully for Tithonus to join the ranks of the immortals. Zeus granted her request. Young love triumphed.
Then the irony set in. What should have been a source of joy for them both turned into a perpetual agony. Tithonus was given eternal life, but not eternal youth. He aged and aged, until he became wizened and frail, hoping every moment for death. No one could commute Zeus's sentence, but, in some legends, Tithonus got turned into a cicada, which still sings with his voice. (In some versions of the legend, Tithonus turns into a cicada naturally, and the rasp of the cicadas is him still begging for death.)
What fun. And it looks like we're now sufficiently advanced that we're granting that fate to roundworms. Specimens of Caenorhabditis elegans were genetically altered, made into mutants with known longevity genes. These specimens were given long lives in a laboratory, next to worms that did not have the same genes to extend their lives. Scientists studied both types of worms as they lived, and found that the ones with the favored genes lived longer.
They did not live better. As they aged, the C elegans with longevity genes were more fragile in the face of heat and oxidative stress, and moved around far less than the worms with regular genes. They got long life, but most of it was lived without strength. Not only did they spend a larger portion of their life old and frail - which is to be expected if they lived longer - they had less overall healthy days than the worms without the longevity genes.
This isn't going to mark the end of the quest for longevity, nor should it. Still, it provides us with something to think about. Scientists want to emphasize this difference between longevity and health. Perhaps we should not be like Aurora, and think of a long lifespan. Instead, we should focus on "healthpan" - the number of years that are active, healthy, and resilient.