Researchers have shown that exercise boosts telomerase and slows the erosion of telomeres with age. Here is another small study that shows the telomere length association: "Telomere length (TL), a measure of replicative senescence, decreases with aging, but the factors involved are incompletely understood. To determine if age-associated reductions in TL are related to habitual endurance exercise and maximal aerobic exercise capacity (maximal oxygen consumption, VO(2)max), we studied groups of young (18 - 32 years) and older (55 - 72 years) sedentary and young and older endurance exercise-trained healthy adults. Leukocyte TL (LTL) was shorter in the older vs. young sedentary adults. LTL of the older endurance-trained adults was approximately [900 base pairs] greater than their sedentary peers and was not significantly different from young exercise-trained adults. LTL was positively related to VO(2)max due to a significant association in older adults. Stepwise multiple regression analysis revealed that VO(2)max independently explained approximately 60% of the variance in LTL. Our results indicate that LTL is preserved in healthy older adults who perform vigorous aerobic exercise and is positively related to maximal aerobic exercise capacity. This may represent a novel molecular mechanism underlying the 'anti-aging' effects of maintaining high aerobic fitness." Equally, it is still plausible that telomere length is only a marker for other processes. Either way, exercise is demonstrably good for your long term health - far better than any supplement or medical technology presently available.

Link: http://www.ncbi.nlm.nih.gov/pubmed/20064545