Researchers collected data on the subjects’ kidney, liver and lung function, dental health, the blood vessels in the eyes as well as their metabolism and immune system function at age 26, 32 and 38. They also measured cholesterol, fitness levels and the length of the telomeres, which are the protective caps at the end of chromosomes that have been found to shorten with age.

Using a total of 18 biological measurements, researchers determined a “biological age” for each participant at age 38 — with some registering under 30 and others appearing to be nearly 60.

When scientists looked closely at the ones who had aged more quickly, they found signs of deterioration were apparent at age 26, the age when the first set of biological measurements were taken. Most of those in the group were aging at the expected rate of one biological year per chronological year, or even less. Others were aging as fast as three biological years per chronological year.