By Professor Ken Purnell and Dr Ragnar Purje
Adolescence is more than just a turbulent few years of high school; it is a lengthy process of brain development that begins around age 9 and continues into the early 30s (Caiafa et al., 2025; Kolk & Rakic, 2022). A 28-year-old’s brain remains more “under construction” than fully developed, especially in areas responsible for planning, impulse control, and complex social judgment (Caiafa et al., 2025; Vásquez-Rodríguez et al., 2019). Long-term neuroimaging and developmental research show that synaptic pruning and structural development of the prefrontal cortex persist steadily into the third decade of life.
Key points
- The brain undergoes an extended adolescence from around age 9 to the early 30s, with a significant shift in network organisation taking place in the early 30s.
- At 30, the brain is still installing its ‘adult operating system,’ especially in networks that support self-control, planning, and complex social judgment.
- Turning 18 doesn’t suddenly make you an adult; the legal age is reached long before the brain fully matures, and growth follows its own timetable rather than the birthday calendar.
- Everyday settings, including relationships, school, work, and digital life, can either strengthen or weaken this developing brain, providing guidance, boundaries, and constructive support. Use of technology is essential throughout the teens and 20s.
The brain’s long adolescent journey
An extensive MRI study tracking 4,216 individuals from birth to age 90 showed that brain development does not follow a smooth, straight path; instead, it passes through specific turning points over the lifespan (Caiafa et al., 2025). One of the most significant events occurs in the early 30s, when the brain’s ‘wiring’ transitions from an adolescent-like, flexible setup to a more stable adult structure (Caiafa et al., 2025).
Between around age 9 and the early 30s, long-range connections between brain regions become faster, stronger, and more efficient, especially in networks responsible for decision-making, self-control, and future planning (Caiafa et al., 2025; Vásquez-Rodríguez et al., 2019).
This extensive development is particularly evident in the prefrontal cortex (PFC), the area behind the forehead that is responsible for planning, impulse control, and complex social reasoning (Kolk & Rakic, 2022).
During adolescence and emerging adulthood, the PFC can sometimes be considered ‘online’ and capable of supporting advanced, logical thinking, and at other times ‘offline,’ when decisions are more influenced by emotion and immediate gratification rather than careful reasoning (Kolk & Rakic, 2022).
In these offline moments, adolescents and young adults may default to ‘what feels good now’ instead of ‘what will work best for later,’ which is why teachers and parents often need to act as a kind of ‘backup PFC,’ guiding decisions, modelling calm thinking, and providing clear, consistent consequences (Maggi et al., 2022; Patterson et al., 1989). Some helpful advice is to do the adult thinking for them, but make sure they believe it is their idea, as ownership matters.
Dopamine, myelin, and the prime time for learning
The brain’s reward circuitry also experiences significant changes during adolescence. Teenagers often display increased sensitivity to dopamine, the chemical messenger that signals reward and motivation, which fuels their pursuit of novelty, intense experiences, and social connections (Kolk & Rakic, 2022). This same sensitivity helps explain their often cheeky sense of humour, which thrives on surprise, incongruity, and playful social interactions.
At the same time, myelin, the insulating layer around nerve fibres, thickens along long-range pathways, enabling signals to travel faster and more reliably between distant regions (Kolk & Rakic, 2022). The combination of dopamine-rich reward systems and increasing myelination makes adolescence and young adulthood a prime period for learning, memory, and skill development: the brain is exceptionally prepared to encode new information, practise complex skills, and reshape habits (Kolk & Rakic, 2022; Vásquez-Rodríguez et al., 2019). This offers excellent prospects for schooling, vocational training, and workplace learning, as the late teens and 20s present a powerful window for building capabilities that will influence the rest of adult life (Caiafa et al., 2025).
Sex differences in timing, not value
Brain development varies among individuals, and longitudinal neuroimaging evidence shows that, on average, females tend to reach some structural and functional brain milestones slightly earlier than males (Lenroot & Giedd, 2010; Sisk & Zehr, 2005).
These are small average differences with significant overlap, and they do not reliably predict any individual’s abilities or future outcomes. Research on cortical thickness and other structural measures, while not entirely uniform across studies, indicates that certain regions, including parts of the prefrontal cortex, generally follow an earlier maturation path in females than in males during adolescence. However, there is considerable overlap and individual variation in both groups (Lenroot & Giedd, 2010).
These biological sex-linked timing patterns at the group level do not mean that one brain is better than the other; instead, they suggest that some neural pathways involved in regulation and planning often appear to reach their peak structure earlier, on average, in females, while similar changes in males tend to occur later in adolescence, with broad variation and substantial contextual influences for everyone (Etchell et al., 2018; Lenroot & Giedd, 2010; Sisk & Zehr, 2005).
For educators and parents, the key message is that expectations and supports should be flexible and responsive, rather than strictly based on age, grade, or biological sex. In any classroom or workplace, the variation among males and among females is usually greater than the differences between them. Therefore, it is more effective to concentrate on individual strengths, needs, and developmental readiness instead of stereotypes related to biological sex or chronological age (Maggi et al., 2022; Rippon et al., 2021).
Responsibility, consequences, and moral development
An extended adolescence can help explain many patterns of teenage and young adult behaviour, but it should not be used to reduce responsibility. Research on play, social behaviour, and moral development shows that children begin understanding choices and their consequences from around three years of age, especially as they participate in social play where actions lead to social outcomes (Maggi et al., 2022).
Through repeated experiences of both positive and negative outcomes, children, adolescents, and adults develop an internal sense of responsibility and a shared understanding of moral and ethical expectations (Maggi et al., 2022; Tangney et al., 2004).
When fair and predictable consequences do not follow antisocial behaviour, it tends to persist and can escalate over time (Patterson et al., 1989). Conversely, environments that combine high expectations with consistent boundaries and strong relationships foster better psychological adjustment, academic achievement, and interpersonal success throughout adolescence and into adulthood (Baumeister et al., 2001; Tangney et al., 2004).
In this context, the developing brain should not be ‘blamed’ when things go wrong; individuals remain responsible for their choices, while adults and institutions share a parallel duty to create environments that encourage wise decisions (Baumeister et al., 2001; Maggi et al., 2022).
Digital life, screen time, and AI
Today’s adolescents are growing up in a digital world that earlier generations did not experience. Extended screen time, especially when dominated by quick reward cycles like social media feeds, gaming, or short-form videos, interacts with the adolescent brain’s heightened sensitivity to novelty, reward, and social feedback (Kolk & Rakic, 2022).
This combination can reinforce habits of seeking rapid stimulation and constant online approval, which may conflict with slower, more deliberate learning and the sustained attention needed for deep study, creativity, and problem-solving (Caiafa et al., 2025).
At the same time, digital tools and AI systems can be valuable allies for learning and wellbeing when used thoughtfully. Well-designed digital environments can support spaced practice, multimodal explanations, and personalised feedback, all of which align with current understanding of how the brain learns best (Kolk & Rakic, 2022).
For teachers and parents, the key question is less ‘how many hours of screen time?’ and more ‘what kind of digital engagement, with what limits, and under whose guidance?’ When adults set clear boundaries, model constructive use, and involve adolescents in open conversations about their digital choices, screens can shift from being a risk factor to becoming tools that foster curiosity, creativity, and responsible decision-making (Baumeister et al., 2001; Tangney et al., 2004).
Why this matters for parents, teachers, and employers
For parents, teachers, and employers, one key message is clear: brain maturity does not always align with legal adulthood (Caiafa et al., 2025; Kolk & Rakic, 2022). A 22-year-old who is at university or in their first job may appear and sound like an adult, but the neural systems responsible for long-term planning, risk assessment, and impulse control are still developing (Caiafa et al., 2025; Vásquez-Rodríguez et al., 2019).
This highlights the importance of ongoing guidance, mentoring, and opportunities for “second chances” during the late teens and into the 20s, without lowering expectations for responsible behaviour.
Seen this way, adolescence and emerging adulthood both serve as warnings and opportunities. They warn us because a highly adaptable brain is more susceptible to stress, substance use, poor sleep, and toxic social environments (Caiafa et al., 2025).
At the same time, they present an opportunity because this same plasticity allows for substantial improvements in learning, emotional regulation, and character when young people are supported with structure, care, and meaningful challenges (Maggi et al., 2022; Tangney et al., 2004).
Conclusion
Growing up is not just a brief phase from 13 to 18, but a lengthy journey of brain development that spans from late childhood into the early 30s. During these years, the brain is constantly wiring and rewiring itself in ways that influence how people think, feel, make decisions, and relate to others, with significant changes in the ‘front’ of the brain and the networks that support adult-like judgment and responsibility. Biology sets a foundation, but everyday environments such as families, schools, workplaces, peers, and digital life play a crucial role in shaping how this development occurs.
For communities striving to nurture capable, caring, and creative adults, this has significant implications. Adolescents and young adults need older individuals who can sometimes act as a ‘backup prefrontal cortex’: offering guidance, boundaries, and wise advice, while still holding them accountable so that responsibility, character, and skills develop together over time.
When this happens, the extended period of adolescent brain development is not a problem to fix but a valuable opportunity. In fact, it is a lengthy, powerful window during which experiences, education, and relationships help shape the kind of adults that families, workplaces, and societies will depend on in the years ahead.
References
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