The Myth of the 25-Year-Old Brain

The Myth of the 25-Year-Old Brain: A powerful idea about human development stormed pop culture and changed how we see one another. It’s mostly bunk.

It's not uncommon for women here to object to age gaps between young women and significantly older men on the basis that "they're too immature because their brains aren't developed until 25", or something along those lines.

Women who say that are just parroting a pop science myth that has little to no basis in reality, for purely ideological reasons.

Maturity is a slippery concept, especially in neuroscience. A banana can be ripe or not, but there’s no single metric to examine to determine a brain’s maturity. In many studies, though, neuroscientists define maturity as the point at which changes in the brain level off. This is the metric researchers considered in determining that the prefrontal cortex continues developing into people’s mid-20s.

That means that for some people, changes in the prefrontal cortex really might plateau around 25—but not for everyone. And the prefrontal cortex is just one area of the brain; researchers homed in on it because it’s a major player in coordinating “higher thought,” but other parts of the brain are also required for a behavior as complex as decision making. The temporal lobe helps process others’ speech and language so you can understand what’s going on, while the occipital lobe allows you to watch for social cues. According to a 2016 Neuron paper by Harvard psychologist Leah Somerville, the structure of these and other brain areas changes at different rates throughout our life span, growing and shrinking; in fact, structural changes in the brain continue far past people’s 20s. “One especially large study showed that for several brain regions, structural growth curves had not plateaued even by the age of 30, the oldest age in their sample,” she wrote. “Other work focused on structural brain measures through adulthood show progressive volumetric changes from ages 15–90 that never ‘level off’ and instead changed constantly throughout the adult phase of life."