Does adolescence last until 32? Scientists unlock brain’s five eras

A new study has found that adolescence can continue until the age of 32, as humans hit four major “turning points” in brain development at the ages of about nine, 32, 66 and 83.

Published on Tuesday in the journal, Nature Communications, the study examined nearly 4,000 scans of the brains of participants ranging in age up to 90.

Researchers mapped out the brain’s development using this data and discovered that humans go through five “brain phases” – and within them, four significant life turning points as they grow, mature and decline.

Importantly, they discovered, it is not until age 32 that human personality and intelligence “plateau” and stabilise following changes in early adolescence.

What are the five phases?

According to the study, brain development and ageing undergo five separate phases:

• Childhood – from birth to age nine
• Adolescence – from nine to 32
• Adulthood – from 32 to 66
• Early ageing – from 66 to 83
• Late ageing – from 83 onwards

When does the brain shift from one phase to the next?

As the brain adapts to new surroundings and situations between birth and old age, researchers found that four ages – nine, 32, 66 and 83 – were the most pivotal in the brain’s development.

The shifts are characterised by developments such as puberty, personality stabilisation, “reorganisation” and decline.

In detail, these are as follows:

Childhood – birth to nine years old

During this period, the grey and white matter of the brain rapidly grow.

According to information from United States-based Johns Hopkins Medicine, while grey matter primarily processes and interprets information, white matter transmits that information to other parts of the nervous system.

“In the brain, grey matter refers to the darker, outer portion, while white matter describes the lighter, inner section underneath,” Johns Hopkins says. “In the spinal cord, this order is reversed: the white matter is on the outside, and the grey matter sits within.”

According to the authors of the new study: “The first few years of life are marked by consolidation and competitive elimination of synapses [the junctions where neurons meet and communicate with each other] and rapid increases in grey and white matter volume.”

“This age also aligns with the onset of puberty, which begins between eight and 13 years old for females and nine and 14 years old for males, marking the initiation of significant alterations in hormone expression and robust neurological changes,” it added.

The report also found that the shift to adolescence introduced an “increased risk” of mental health, cognitive and behavioural disorders due to changes in hormones and a “neurobiological shift”.

Adolescence – 9 to 32

Previously, it was accepted that adolescence begins with puberty and ends before the age of 20. However, the study found that while adolescence certainly begins with puberty, its ending point is less clear.

“The transition to adulthood is influenced by cultural, historical and social factors, making it context-dependent rather than a purely biological shift,” the researchers found.

“Our findings suggest that in Western countries (ie, the United Kingdom and United States of America), adolescent topological development extends to around 32 years old, before brain networks begin a new trajectory of topological development,” they added.

The study found that by age 32 in Western countries, the brain experiences the “most directional changes and a large shift in trajectory” compared with other turning points in life, as this is when white matter integrity and volume in the brain are increasing rapidly.

The authors did not suggest a reason for this being the case in Western countries, and did not elaborate on how adolescence continues in people in other regions of the world.

Adulthood – 32 to 66

The study found that while brain development rapidly accelerates during the first two phases of life, in adulthood – the longest phase – there are no major turning points until the 60s, as the brain develops more slowly.

“This period of network stability also corresponds with a plateau in intelligence and personality,” it found.

Early ageing – 66 to 83

While the brain does not show any abrupt signs of decline during this phase, shifts in the patterns of connection in the brain do occur due to a decrease in white matter integrity.

The brain now works more independently in separate regions, coordinating less as a single whole.

The early 60s mark an important shift in health and cognition, with the onset of dementia and elevated blood pressure for many, both of which can accelerate brain ageing.

Late ageing – 83 onwards

While there is less data on this era of the brain’s progression than the other phases due to a low sample size, the study’s findings correlated with a declining trend in brain connectivity, the authors said.

“Therefore, this could reflect a true weakening relationship between age and structural brain topology in late life,” they added.

Why is this significant?

The new research into the period of adolescence is the most significant finding from the report.

According to the World Health Organization, adolescence ranges from 10 to 19 years of age. In 2018, a report in The Lancet medical journal found that adolescence ended in the 20s.

But Duncan Astle, professor of neuroinformatics at Cambridge University in England and one of the authors of the study, told The Independent newspaper that the new report helps us better understand the brain’s vulnerabilities.

“Looking back, many of us feel our lives have been characterised by different phases. It turns out that brains also go through these eras,” he said.