People in their 20s could accurately be described as "kidults", according to research that suggests adolescent effects on the brain extend far beyond the early teens.
The brain changes increase a desire for sensation-seeking and novelty and evolved to help us leave the safety of the nest and fend for ourselves, US psychiatrist Beatriz Luna believes.
Previously they were thought to peak at age 15.
But studies conducted by Prof Luna, from the Pittsburgh School of Medicine, indicate this is far from the case.
Specifically, she has found evidence of hyper-activity in the striatum, an area of the brain stimulated by "rewards" that seems to continue well into the 20s.
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What appears to bring the process to a halt is the shouldering of "adult" responsibilities such as holding down a job, paying a mortgage and raising a family.
Asked when she thought people truly crossed over the threshold of adulthood, Prof Luna said: "It's probably closer to 25."
She said in teenagers the sensation-seeking part of the brain worked in conjunction with the "planning centre", the pre-frontal cortex, to drive curiosity and experimentation.
Speaking at the American Association for the Advancement of Science (AAAS) annual meeting in San Jose, California, Prof Luna explained: "Sensation seeking, which is really information seeking, novelty seeking, is evident across species and human societies.
"I'm saying this is combining with a brand new shiny car called the pre-frontal cortex. The adolescent is, like, 'Oh, this is great, I can plan', but they're doing it in the service of this heightened sensitivity to motivation."
It was a system that allowed the adolescent "not to ask mummy and daddy" but to seek out novel situations.
She said she was still conducting research to find out how far into adulthood the brain changes continued, but they could possibly carry on into a person's 30s.
The rewiring was part of a process of "specialisation" that could be compared with a sculptor hewing a finished shape out of a piece of granite or marble.
