Sarah-Jayne Blakemore in Edge:
This was about 12 years ago. Back then, I delved into the literature and, to my surprise, there was little known about how the human teenage brain develops. There were a handful of studies back in the year 2002, a small handful, but they were intriguing because even though there were only a few of them, they all pointed to significant and protracted development of the brain right throughout adolescence and into the 20s. This was an interesting finding because, prior to those papers, most neuroscientists would have assumed, and the dogma at the time I was an undergraduate and a graduate, was that the human brain stops developing some time in childhood and doesn't change much after mid to late-childhood. What these papers suggested was that the dogma was completely wrong. In fact, the human brain continues to develop significantly across almost the whole cortex throughout the teenage years, and even into the 20s.
More here.