Your cells might be aging faster than you are, and new tests purport to help you find out.

A few companies are offering mail-order testing to measure the length of people’s telomeres, the protective caps of DNA on the ends of chromosomes that have been likened to the plastic tips that prevent shoelaces from fraying. Telomeres gradually shorten as people age and eventually may disappear, leaving cells vulnerable to disease and death.

Telomere Diagnostics, of Menlo Park, Calif., launched an $89 test last week. Users mail in a drop of blood and get back a calculation of their age in “TeloYears,” adjusted up or down depending on how they compare with the general population. The service also provides advice for improving diet, fitness, sleep and stress levels, which some small studies suggest may help telomeres regain length.

“There’s a difference between knowing how old you are, and how well you are aging,” says Telomere Diagnostics chief executive Jason Shelton. “The age you are on the inside, on the cellular level, may be a better indicator.”

Still, some top telomere scientists say such information amounts to little more than high-tech palm reading, in part because telomere length varies so widely in the general population that it isn’t clear what length is problematic.