A new study out of New Zealand has confirmed what you may have already intuited-- different people age at vastly different rates. After all, we all have friends who appear to be younger or older than their chronological age. According to this study, that’s because although most humans age one biological year for each of their chronological years, some age more slowly, and some age up to three biological years per chronological year.

The study looked at 954 New Zealanders born between 1972 and ‘73. At age 26, 32, and 38 each subject was measured for a variety of aging related characteristics, such as telomere length, cholesterol levels, and overall fitness. At age 38, it was found that some of the subjects had all the characteristics and therefore the biological age of someone under 30. But others had the biological age of someone in their late 50s.

When university students were given pictures of the subjects and told to guess their age, they consistently guessed that the biologically older subjects were older. And when the “older” subjects were tested on things such as mobility, balance, and coordination, they scored worse than their peers.

Unfortunately, the study has not yet yielded any practical advice. But the scientists behind it plan to continue this line of research. “This is just the beginning,” said lead scientist Daniel Belsky. “The next step is to… identify the causes of accelerated aging so that we might slow it down.”