The "brain matures at 25" myth or "twenty-five year old brain" myth is the claim that the human brain, particularly the prefrontal cortex, reaches an adult level maturity approximately around age 25. This myth occasionally has others numbers cited, but 25 is by far the most commonly occurring. Teen brain theory is the pseudoscientific theory based on this myth.^[1] The myth suggests that a person does not have full adult capacity or maturity until this age threshold is achieved. It has been attributed to various figures, notably Jay Giedd and Laurence Steinberg.

It has been shown that the prefrontal cortex does prune gray matter with age, but these changes are not conclusively linked with better cognitive function or a higher level of socioemotional maturity. It is widely quoted on social media outlets, usually in debates regarding legal age limits or youth behavior.

A common source for the myth is from the research of Jay Giedd. The study in particular was longitudinal, following a group of thirteen people from 1994 to 2004 with ages at the end of the study ranging from 4–21 years old. His team of researchers found that changes in the prefrontal cortex were found to continue up until the oldest age in the study.^[2] He estimated that this "age of maturity" would be around 25 years old. "When we started, we thought we'd follow kids until about 18 or 20. If we had to pick a number now, we'd probably go to age 25."^[3] There were also other very similar articles predating 2004 that often used the work of Giedd along with neuroscientists Frances Jensen and BJ Casey, usually using the development of the prefrontal cortex as a scientific explanation for "teenage behavior."

The work of Laurence Steinberg is also purported to a significant amount of influence in the spreading of this myth. His research generally focuses around adolescent brain development and risk-development and is generally used to influence the juvenile justice system and provide lighter sentences for offending youth.^[4] He proposes the science of neuroplasticity should redefine how society treats "adolescents" and that a specific range of 10- to 25-year-olds have undeveloped brains.^[5] He would later say, in a 2022 article, that he was not sure where the "25" number came from in regards to the age of brain maturity.^[6]

There is historical precedent for claiming the twenties to be part of "adolescence". Around 1900, psychologist G. Stanley Hall considered youth to be roughly ages 12–21 for females and 14–25 for males.^[7] He tied it to being a stage of "storm and stress"; he noted higher crime rates, sensation seeking, susceptibility to media, and sensitivity to peer relationships, but later psychologists consider other major points outdated, such as his views on Lamarckian evolution, sexual development, and religious conversion.^[8]

The development of the brain is a lifelong process. Maturity is assessed via structural MRI (gray/white matter volume, cortical thickness), functional MRI (activation patterns), and diffusion tensor imaging (myelination/connectivity). These processes do not peak or end at 25 and no executive function changes are found around this age.^[9][10]

Empirical data on youth risk varies, but individual differences matter more than chronological age. Equating structural changes with behavioral "immaturity" risks oversimplification; adolescents often have adult-like performance on many tasks.^[11] A major study (2025) identifies distinct developmental epochs in brain network organization across the lifespan, showing that maturation unfolds in phases with a prolonged and dynamic period extending into the early 30s rather than ending in the mid-20s. They found an epoch of 9–32 years of age. A study from 2023 found that brain signal latencies decrease across the lifespan by 0.73 ms until the age of 10, while decreasing by 0.43 ms between the ages of 20 and 30, with latency decreases ending at around 35 years of age or older. ^[12]

It is not supported that marijuana use impairs cognitive function of those 18–25 more than it does those older than 25.^[13]

The "brain matures at 25" myth is often the source of memes where the "immature frontal lobe" is used to excuse personal mistakes and poor judgement. The myth is also used in age-gap relationship discourse regarding the morality of being with a younger person.^[14] It is also commonly used as a form of ridicule against Leonardo DiCaprio's relationship patterns where his partner is usually no older than 25 years old.^[15]