When a person reaches adulthood, their brain is the biggest it’ll ever be. As age progresses, human brains tend to shrink a bit from their peak, and that’s something that has been known for some time. However, there’s a significant difference between men and women in terms of brain “age” as we all grow older.

In a new study published in the Proceedings of the National Academy of Sciences, researchers from Washington University School of Medicine in St. Louis explain that women’s brains tend to remain younger than their male counterparts even when both individuals are the same age. But what’s particularly interesting is the scientists were even able to calculate how much older male brains are.

The researchers, led by Dr. Manu Goyal, closely studied the brains of over 200 individuals in the search for answers. The participants ranged in age from 20 to 82. The team studied each person’s brain using scans that offered insights into how much oxygen and glucose the organs were using. These measurements told the researchers the metabolic “age” of the brains, which could then be compared to the age of each person.

When the team crunched the numbers they discovered that the metabolic age of the brains in women were on average 3.8 years younger than the brains of men at the same ages.

The data was consistent across the board, and it’s clear that there’s a key difference between the brains of men and women. However, it’s still unclear exactly what mechanisms play a role. The researchers assert that male brains reach their peak three to four years earlier than female brains, and that difference is carried on throughout their lives. Why that is, and whether it could be significant for research into disease like Alzheimer’s, will require further research.