Myth busted: the idea the brain doesn’t fully develop until 25 is wrong

There’s a popular and trusted adage that is often used to discount the contributions of young people and forgive them for their mistakes.

It has been cited in government recommendations, gun ownership discourse and sentencing laws. It has featured as an explanation for school shootings and as an argument against lowering the voting age.

The human brain does not reach full developments at the age of 25.Credit: Getty Images

It has also formed the longstanding basis of my mother’s reluctance to let me ride a motorbike.

You might have heard it: “The human brain does not develop fully until 25.”

Often referenced at the first hint of rebelliousness in young people, it suggests that those under 25 are impeded or immature in their decision-making – after all, their underdeveloped brains mean their reasoning is less sound, right?

Wrong.

Neuroscientist and bestselling author Dean Burnett this year revealed that there is no justification for the idea. It’s likely a misunderstanding rooted in studies that only considered subjects aged 25 and under – “but that’s like saying sprinters can only run 100 metres at most after watching the 100-metre final at the Olympics,” Burnett says. “The limit is imposed by the context, not the biology.”

Taking this further, scientists Richard Bethlehem and Jakob Seidlitz, who surveyed over 123,000 brain MRI scans, told IFLScience that it’s “very unlikely” any blanket rule for brain growth and change could be formulated at all.

On the back of this research, some experts now suggest that brain development likely never stops, with neural connections being made constantly. No matter our age, we’re all developing (and degenerating) – meaning that learning and making mistakes are not just for the young.

The ramifications of this revelation go beyond science. It challenges the way our society perceives age.

If we accept that we don’t just ”tick over” into maturity, the idea that 18 should be the default age to drink, buy cigarettes, drive, vote and gamble begins to seem arbitrary.

Victorian medical consent laws for children present a more nuanced alternative. Rather than focusing entirely on age as the indicator of a patient’s right to make decisions, medical professionals consider children’s demonstrated comprehension of procedural consequences. This framework, based on individual capacity, might not be feasible or appropriate for processes like voting, but it’s far less arbitrary.

A developing mind is not necessarily one that doesn’t function well, by the way. Burnett compares stages of development to evolution; at each stage is a fully functioning, reasoning species.

In light of this, perhaps more credence should be given to young people’s opinions and insights, to our often valid ideas and judgments. The School Strike 4 Climate movement, for example, might not be the ravings of kids reluctant to sit through period five maths, but instead the legitimate, well-reasoned complaints of a competent group.

And without immaturity as an excuse, we might also deserve less leniency. The year 11 boys who ranked female classmates from “wifey” to “unrapable” don’t have the automatic defence of “still developing”. Nor do schoolboys chanting sexist rhymes on public transport, or high school students who ruthlessly bully their peers.

Sure, the issue in those cases might be about experience rather than maturity. Though, by the final years of school, it’s hard to argue that kids haven’t lived long enough to realise they should treat one another respectfully.

The argument that young people can’t always make sound decisions is often based on our being emotional, mistake-prone and rebellious. Burnett, however, argues that this is no sign of immaturity. “If certain members of your population, particularly ones in their physical prime, tend to reject the norms and wander off to try new things, that’ll stave off stagnation,” he says.

The consequences of Burnett’s findings go on. But the crux is this: with our brains developing throughout our lives, young and old have more in common than we would like to admit.

Daniel Cash is a law student at ANU.

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