I’m sure you’ve heard that we should give teenagers a break when they make really dumb decisions because their brains aren’t fully developed.

Is it true, though? And is 25 really a magical number when everything up there clicks?

The short answer is no, because as this 2013 paper notes, the brain continues to grow and change for a long time.

“The notion that brain development is not complete until near the age of 25 years refers specifically to the development of the prefrontal cortex. That’s part of the frontal lobe, sometimes referred to as the “rational part” of the brain.”

Neuroscientist Shannon Odell explained more in a Ted-Ed video.

“The prefrontal cortex, a brain region responsible for cognitive control and inhibition, is slower to develop. Adults benefit from a well-developed prefrontal cortex, allowing them to better execute skills that require learning, focus, and memory.”

In truth, 25 might be an average, but in real life, the dorsal-lateral prefrontal cortex timeline of development is going to vary significantly between individuals.

In general, it will be complete a year or two earlier in women, but more than that, one researcher says there is “no proven correlation between brain changes and behavior.”

In a 2022 paper researchers made charts of how the human brain grows over a lifetime. They did this by looking at the volumes of different tissues in the brain scans of more than 100,000 participants.

Their ages ranged from 115 days post-conception to 100 years.

“We generally have an understanding of how big the human brain is, but we have never been able to measure this with such precision or at such a large scale across the whole lifespan.”

In fact, trying to understand it might be a futile effort, according to the authors.

“There is no single dataset that could answer this question. It has been only through this truly global effort that we have been able to virtually ‘stitch’ together dozens of neuroimaging datasets at a massive scale. What we additionally provide on top of that is a standard blueprint for how the brain typically develops and a common language in terms of converting brain measures into percentile scores.”

The data can tell us something about how the brain develops in our younger years compared to its later stages of life.

“Perhaps somewhat unsurprisingly we find that most basic morphological properties that we measure have their peak early on in development, many even before the sixth year of life. So changes are much more rapid early on in development, while in later stages of life the changes are more subtle and gradual. We find that the individual variability is highest in adolescence and young adulthood (when individuals with psychiatric disorders are typically diagnosed).

They warn, though, that it’s “very unlikely” science will ever be able to come up with a one-size-fits-all timeline for brain development.

“We find that not only is there enormous inter-individual variability but also that it really depends on the specific property that you are measuring and in what part of the brain you are measuring it. We also acknowledge that even with 125,000 scans we don’t have a full and comprehensive picture of the true variation in the population as these are still biased toward WEIRD (Western, Educated, Industrialized, Rich, and Democratic) countries where a lot of this research is done.”

They are still working to put together a list of relative developmental milestones, though.

“There is a lot of research happening (not least in our collaborative network) to see whether some of the developmental milestones we identify intersect with milestones of cognitive development. There is also a large field of research trying to pinpoint specific cognitive domains and functions to specific maturational patterns of different brain systems. There is probably an association between how we think and how our brain develops and is organized, but to make studying this practically feasible we tend to break this down into smaller chunks of specific cognitive processes and specific properties of the brain.”

And what about the age of 25?

They say it’s relevant, but not exact.

“The mid-twenties number doesn’t come entirely out of the blue as it is an age where many different brain regions will have reached their maximum volume for example. However, this absolutely does not imply that the brain then stops being malleable to change nor does it mean that up until that point the brain would not be capable of functioning at a developed level.”

So, by the age of 25, most of us will be able to have full control of our prefrontal cortex.

For others, it might be a few years earlier, or a few years later.

Either way, you’ll have to start taking credit for your own bad decisions.

By the time you’re 30 for sure.

If you found that story interesting, learn more about why people often wake up around 3 AM and keep doing it for life.