One current theory of aging says telomere length determines the rate of cellular aging. If we could find a strong connection between aerobic fitness and increased telomere length, then we would have another tool in our antiaging kit.
Studies connecting cardiovascular fitness and telomere length have been conflicting. Some have shown that exercise does have a protective effect on telomeres (and therefore the rate of aging), while others have shown no association.
This small study of 10 young and 10 older men sought to find a relationship between VO2max and telomere length. The groups were comprised of endurance athletes and medium exercisers.
It did find a relationship between long term endurance exercisers (older men) and telomere length, but not with the younger group.
To me this is not a large enough study to say “It is desirable not just to exercise but become an endurance athlete”. This would not only be a huge commitment of time and energy, but it isn’t really clear from this study whether aerobic capacity developed late in life would be sufficient to provide this protective effect.