Ever suspect that you’re secretly younger (or older) than someone your exact same age? Well, you probably are. (Photo: Getty Images)

Looking at your classmates in 20 years’ time, you might notice something odd about their appearances: Although you were probably all born within a year of one another, you also probably all look different ages. According to new research published in the Proceedings of the National Academy of Sciences, internal markers show we really do age at different paces.

The data for this research was taken as part of the Dunedin study, a longitudinal research project where the health of around 1,000 men and women from Dunedin, New Zealand, has been monitored from their birth, in 1972 and 1973, until now.

For the current research, scientists from the United States, United Kingdom, Israel, and New Zealand looked at 18 biological markers of these men and women for the effects of aging. The measurements included kidney, liver, lung, metabolic, and immune function, along with HDL cholesterol, cardiorespiratory fitness, dental health, blood vessel condition, and telomere length.

Taking all the biological markers into account, the scientists set a “biological age” for each person in the study at age 38 in 2011, placing it on a timeline from under age 30 to over age 60. Then the researchers compared the results to the same measurements taken at ages 26 and 32 so they could track how quickly each participant was aging.

As the researchers guessed, those who had older biological ages at age 38 seemed to be aging faster than their peers. For most, the aging rate was roughly one year per year, but some were aging at a rate of up to three years per one year, and others were actually aging closer to zero years per one year.

Men and women who fared worse on the biological measurements for aging also performed worse on tests typically given to the elderly, like those of balance and coordination. In addition, when Duke undergrads were recruited to guess the real-time ages of the participants, they presumed that those who were aging faster biologically were older.

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Aging isn’t like winning a genetic lottery, according to the researchers. Past studies of twins have shown aging is only about 20 percent genes, leaving a lot of room for other factors. Although this test didn’t answer the question of why some age quicker than others, the researchers are now looking into it, says lead study author Daniel Belsky, an assistant professor of geriatrics at Duke University’s Center for the Study of Aging and Human Development.

“I think the three general categories of factors that people think about in research on aging are genetics, early-life experiences like chronic stress or trauma, and lifestyle factors like diet and exercise,” Belsky tells Yahoo Health.

Going forward, Belsky says, this research can contribute in a few key ways. “First, measurements of the aging process allow us to begin asking questions about what might cause accelerated aging,” he says. “We can compare people who have different life histories, who engage in different kinds of behaviors, and who live in different environments to test if any of these factors contribute to differences in aging rates.”

Belsky also says determining “pace of aging” can be highly useful, because these measurements can test the effectiveness of therapies directly aimed at preventing disease by slowing the aging process. “Currently, such evaluations require very long follow-up times because we have to wait and see if people develop chronic disease or die prematurely,” he says. “Using measurements like our ‘pace of aging,’ it is possible to test the effectiveness of therapies to slow aging in real time.”

In addition to testing therapies, Belsky also thinks “pace of aging” can be used in clinical settings to improve doctor-patient communication about health risks. “Rather than discussing a large number of different measurements taken in the course of a physical exam, a doctor could begin by discussing just one number — Pace of Aging or Biological Age,” says Belsky. “There is still much work to be done to get to this point, but that’s where we are headed.”

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