The teenage years turn out to be a complicated time in the brain, with cells fighting it out for survival and the connections between different regions being rewired and upgraded. Some abilities, such as quashing offensive behaviour and empathizing with others, keep maturing well into the twenties. The passage from childhood to adulthood is not straightforward: some researchers now see the teenage remodelling as analogous to the 'developmental window' that allows the brain to be moulded by experience in infancy. There are ways in which teenage brains perform quite differently from either childish or adult ones.
The prefrontal cortex mentioned in the article is basically the part of the brain that keeps you from doing what you desperately want even though you know it is inappropriate -- whether that be strangling your boss or me turning around and methodically stuffing an entire popcorn bucket into those teenager's wagging jaws. (I assert that the fact that I have not been arrested for doing this is a testament to my fully functioning prefrontal cortex.) Research shows that the prefrontal cortex is one of the very last places for the grey matter (the part with the neurons) to mature.
I also notice a degradation as people grow older.