Average telomere length in cells reflects some combination of cell division rates and cell replacement rates: telomeres shorten with each cell division until cells self-destruct because telomeres are too short, and replacements are generated with long telomeres by stem cells. The stem cell activity that delivers those replacements tends to decline with age, and so average telomere length tends to decrease as well. But this is highly variable between individuals and with circumstances such as illness, exercise, and so forth. Researchers only see the decline in statistics gathered across a large study population, making this a terrible measure of aging for any individual consideration. Added to this, for every paper to show some useful correlation for telomere length, there is another to show no useful correlation between teleomere length and measures of aging, such as this one that examines natural variations in telomere length and longevity in nematode worms:
Telomeres are involved in the maintenance of chromosomes and the prevention of genome instability. Despite this central importance, significant variation in telomere length has been observed in a variety of organisms. The genetic determinants of telomere-length variation and their effects on organismal fitness are largely unexplored. Here, we describe natural variation in telomere length across the Caenorhabditis elegans species. We identify a large-effect variant that contributes to differences in telomere length. The variant alters the conserved oligonucleotide/oligosaccharide-binding fold of protection of telomeres 2 (POT-2), a homolog of a human telomere-capping shelterin complex subunit. Mutations within this domain likely reduce the ability of POT-2 to bind telomeric DNA, thereby increasing telomere length.
Our observation that considerable telomere-length variation in the wild isolate population exists allowed us to directly test whether variation in telomere length contributes to organismal fitness. We did not see any correlation between telomere length and offspring production, suggesting that fitness in wild strains is not related to telomere length. In contrast to findings in human studies, we did not identify a relationship between telomere length and longevity. Our results confirm past findings that telomere length is not associated with longevity in a small number of C. elegans wild isolates or laboratory mutants. In summary, this study demonstrates that a variant in pot-2 likely contributes to phenotypic differences in telomere length among wild isolates of C. elegans. The absence of evidence for selection on the alternative alleles at the pot-2 locus and the lack of strong effects on organismal fitness traits suggest that differences in telomere length do not substantially affect individuals at least under laboratory growth conditions.