It's not that aging doesn't leave a variety of biological clues. Over the years, lung capacity tends to decrease, eyesight and hearing worsen, skin loses its elasticity, and telomeres, the DNA caps at the ends of chromosomes, shorten as a result of many cycles of cell division. But although these dreaded indicators show up in almost everyone sooner or later, they don't seem to happen at a set time. A countless number of factors influence the aging process, most notably one's
genetic history, socioeconomic status and personal habits. Until we better understand the intricacies of aging, there will be no algorithm, no deterministic way for a doctor to enter a
set of facts and a blood test into a computer and have it spit out an age. Life, to put it simply, is too complex.