Girls may mature faster than boys, but women's brains are apparently biologically younger than men's of the same age.

In a new study published in the journal Proceedings of the National Academy of Sciences on Feb. 4, researchers revealed their findings from the analysis of the brain scans of over 200 adults. Scientists discovered, after studying a measure of the brain's metabolism that is known to change with age, that on average, women's brains appeared around three years younger than men's brains of the same chronological age.

The age of the brain can be determined by its metabolism, specifically the movement of glucose, the brain's major fuel source. In young brains, more glucose is devoted to aerobic glycolysis, a metabolic process thought to help with brain development and maturation, including brain-cell growth. However, aerobic glycolysis lessens as people grow older, and it usually drops to very low levels by the time they reach their 60s.

For this study, researchers studied the difference between men and women in terms of brain metabolism, analyzing brain-imaging scans of 84 men and 121 women whose ages ranged from 20 to 82 years old. Using a machine-learning algorithm, scientists found that women's brain-metabolic ages were 3.8 years younger than their chronological age.

However, when they calculated the brain ages for men, they found that men's brains were around 2.4 years older than their actual age.

The gap in brain ages between men and women was detectable even in young adults in their 20s. "It's not that men's brains age faster — they start adulthood about three years older than women, and that persists throughout life," Dr. Manu Goyal, senior study author and an assistant professor of radiology at Washington University School of Medicine in St. Louis, said in a statement.

This new research will still need follow-up studies in order for the findings to be considered conclusive. However, the findings, if proven to be true, could explain why women's thinking abilities do not decline as much as men's as they grow older, according to Goyal.

"What we don't know is what it means," Goyal said. "I think this could mean that the reason women don't experience as much cognitive decline in later years is because their brains are effectively younger, and we're currently working on a study to confirm that."