Determining chronological is easy -- count forward from birth. But determining physiological age has remains subjective, based on how someone looks or functions.
Researchers studying genes believe they can now detect your exact "physical age" by looking at a number of clues in your DNA. They believe that the tests will be the first time doctors can accurately predict someone's physiological age objectively, without resorting to asking them how they feel or looking at their appearance.
This could solve the mystery of why some 70-year-olds function at the level of those in their 50’s, while others become frail sooner than would be expected.
The researchers made the breakthrough by isolating the "biomarkers" of aging in tiny worms which behave similarly to humans.