Scroll through TikTok or Instagram and you will likely see the familiar line: “Your frontal lobe isn’t fully developed yet.” It has become a popular explanation for questionable choices, from ordering another drink to texting someone you promised to avoid.
The frontal lobe is responsible for many higher level abilities, including planning, decision making, judgment, and emotional control. Because of that, it is often blamed when we act impulsively or feel unsure of ourselves.
For many people in their 20s and early 30s, the idea is comforting. If life feels messy or unstable, it is reassuring to think biology is partly responsible. The belief that your brain is still unfinished can make uncertainty feel normal.
However, the widely repeated claim that brain development, especially in the frontal lobe, stops at 25 is not accurate. While it is based on real scientific findings, it simplifies a much longer and more complicated developmental timeline. Newer research indicates that important changes continue into our 30s, suggesting that 25 was never meant to mark the end of brain maturation.
How the Age 25 Brain Myth Started
The focus on 25 traces back to brain imaging studies conducted in the late 1990s and early 2000s. In a 1999 study, scientists repeatedly scanned the brains of children and teenagers to observe changes over time. They examined grey matter, which consists of neuron cell bodies and is often described as the brain’s “thinking” tissue.
During adolescence, grey matter undergoes pruning. Early in life, the brain forms a vast number of neural connections. As we grow older, connections that are used less frequently are reduced, while frequently used pathways are strengthened. These shifts in grey matter volume were identified as a key part of healthy brain development.
In later research led by neuroscientist Nitin Gogtay, participants as young as four were scanned every two years. The results showed that areas within the frontal lobe mature gradually from the back toward the front. Regions involved in basic functions, such as voluntary movement, develop earlier. More complex areas tied to judgment, emotional regulation, and social behavior were still maturing by the last scans at about age 20.
Because the data collection ended around age 20, researchers could not pinpoint when development was complete. Age 25 became a rough estimate for when maturation might finish. Over time, that estimate solidified into a widely accepted belief.
Brain Network Development Into the 30s
Neuroscience has advanced significantly since those early studies. Instead of examining single brain regions in isolation, researchers now focus on how different areas communicate and form networks.
A recent major study assessed efficiency of brain networks, essentially how the brain is wired, through white matter topology. White matter is made up of long nerve fibres that link different parts of the brain and spinal cord, allowing electrical signals to travel back and forth.
Researchers analyzed scans from more than 4,200 people from infancy to 90 years old and found several key periods of development including one from age nine to 32, which they coined the “adolescent” period.
For anyone well into adulthood, it may feel jarring to be told that your brain is still an “adolescent,” but this term really just signifies that your brain is in a stage of key changes.
Based on this study, it seems that during brain adolescence, the brain is balancing two key processes: segregation and integration. Segregation involves building neighbourhoods of related thoughts. Integration involves building highways to connect those neighbourhoods. The research suggests this construction doesn’t stabilize into an “adult” pattern until the early 30s.
The study also found that “small worldness” (a measure of network efficiency) was the largest predictor for identifying brain age in this group. Think of this like a transit system. Some routes require stops and transfers. Increasing “small worldness” is like adding express lanes. Essentially, more complex thoughts now have more efficient paths throughout the brain.
However, this construction doesn’t last forever. After around the age of 32, there is a literal turning point where these developmental trends switch directions. The brain stops prioritizing these “expressways” and shifts back to segregation to lock in the pathways our brains use most.
In other words, your teens and 20s are spent connecting the brain, and your 30s are about settling down and maintaining your most used routes.
Neuroplasticity and Building a Stronger Brain
If our brains are still under construction throughout our 20s, how do we make sure we are building the best possible structure? One answer lies in boosting neuroplasticity — the brain’s ability to rewire itself.
While the brain remains changeable throughout life, the window from age nine to 32 represents a prime opportunity for structural growth. Research suggests there are many ways to support neuroplasticity.
High-intensity aerobic exercise, learning new languages and taking on cognitively demanding hobbies like chess can bolster your brain’s neuroplastic abilities, while things like chronic stress can hinder it. If you want a high-performance brain in your 30s, it helps to challenge it in your 20s, but it’s never too late to start.
There is no magical switch that turns on at age 25, or even 32 for that matter. Like your brain, you’re in a decades-long construction project. Stop waiting for the moment you become an adult and start making active choices about how to support this project. Make mistakes, but know that the concrete hasn’t set quite yet.
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