Laufs said he can't prove that the association has anything to do with cause and effect: Did a lifetime devoted to exercise make the 50-year-old marathon runners biologically younger, or did these individuals inherit physical advantage to begin with that would have made them appear biologically younger and led them to exercise more?
"This type of conclusion cannot be made," said Laufs, especially because "the people we looked at in this study are kind of extreme examples. We chose these extreme examples because we wanted to look at the mechanism."
For the rest of us who don't run marathons until we're 50, exercise experts ask that we please keep trying.
"To a very, scientific level and an applied level there are really two tracks that we have to pursue. One is to understand the mechanisms by which exercise helps," said Michael E. Rogers, professor and Chair of Human Performance Studies at Wichita State University in Kansas.
"The other track is to take that knowledge to make it applicable to people," he said.
Rogers argues that science has already found ways to prolong life, but that many can't enjoy them because they didn't stay healthy through exercise in their older years.
"Exercise is not just about living longer, there's a difference between quality and quantity of life. We've gotten to the point with technology where we can extend someone's life long after they can be physically active," he said. "I don't think any one of us wants to live an extra 10 years supported by machines, we want to avoid that."