The Truth About Brain Development: When Do We Really Become Adults?

For a long time, it was believed that the prefrontal cortex—the part of our brain responsible for decision-making and impulse control—didn’t fully develop until the age of 25, which is when we’d become proper adults, basically. But this isn’t actually true; it was an oft-repeated myth that probably stemmed from an old study in which scientists looked at brain scans up until the age of 25. But no matter. We heard “25” and we ran with it. Probably because it sounded good. We were all dumb at 23, right?

That said, if you’re interested in when the brain truly does reach a certain level of maturity, a new study (not just an overzealous TikToker) may have quite a solid answer. According to researchers at the University of Cambridge, who scanned the brains of around 4,000 people between the ages of zero and 90, the brain stays in its adolescent phase up until… our early 30s, which is when we “peak.” That’s right: we’re not adults until we’re approximately 32. Good news for those who don’t have everything figured out at 28, then. You have time!

In the study, which was published by Nature Communications, the brain evolves in five broad phases throughout our lives, split up by four pivotal “turning points.” The “childhood brain” runs from birth until a turning point at the age of nine, when it transitions to the “adolescent” phase—an era that lasts right up until the age of 32, on average.

“Our early thirties see the brain’s neural wiring shift into adult mode,” writes Fred Lewsey at the University of Cambridge. “This is the longest era, which lasts over three decades. A third turning point around age 66 marks the start of an ‘early ageing’ phase of brain architecture. Finally, the ‘late ageing’ brain takes shape at around 83 years old.”

This study is quite a big deal, it turns out. “This study is the first to identify major phases of brain wiring across a human lifespan,” says Dr. Alexa Mousley, a Gates Cambridge Scholar who led the research, adding that, “These eras provide important context for what our brains might be best at, or more vulnerable to, at different stages of our lives.”

Don’t get too excited, though—it’s not like you suddenly become much smarter or more logical at the magical age of 32, which is what one might hope if you are—cough – hovering around that age, like some of us. It would be more accurate to say that the brain’s architecture stabilizes around this time, and it doesn’t hugely change again for another 30 years. This corresponds with a “plateau in intelligence and personality” based on other studies, say researchers. So, maybe it’s not so good after all?