If you’re in your 30s, you probably remember the point when your friends’ appearances started to diverge. Your best friend from elementary school has gone completely gray, but that girl you knew in college still looks like she just turned 18. According to a recent study, there’s a scientific explanation for this phenomenon — biological markers of early aging begin appearing as often as the mid-20s.

The new findings come from a longitudinal health study conducted in New Zealand from 1972 to the present, following 954 subjects throughout their lives. Health data related to aging, including dental health, metabolism, immune function, cholesterol, fitness levels and telomere length were collected at ages 26, 32 and 38. The researchers used this data to estimate a “biological age” for each participant.

They found that there was significant variation in biological age between the participants, with the first signs of divergence appearing in the data collected at 26. By 38, some of the participants’ biological ages still came in at under 30 years, while others clocked in at nearly 60. The researchers found that these biologically older people were aging at a rate of up to three biological years per calendar year.

So are these differences visible from the outside? According to the study, they are — people shown images of the participants at the same age reliably guessed that the people who were found to be aging faster were older than those who had fewer markers of aging.

“Most studies of aging look at seniors, but if we want to be able to prevent age-related disease, we’re going to have to start studying aging in young people,” lead author Dan Belsky of Duke University said.

For information on how you can age gracefully, contact the Longevity Centres of America today.