Science has proven that girls do in fact mature more quickly than boys, and by a pretty wide margin. The brains of females can start developing up to a decade earlier than their male counterparts. This was learned by accident when researchers at New Castle University were studying a separate matter of brain development in information storage. Primarily they discovered that as the developing brain fine tunes itself, it becomes more depth at storing important information and discarding superfluous data.
That process is vital to the formation of organized and efficient neural networks. It's also thought to be what gives girls earlier access to many cognitive and emotional abilities. They also stumbled upon the fact that the maturation process begins in girls as early as 10 years of age. Boys on the other hand don't typically enter that stage until between the ages of 15-20.
For the experiment at large, they monitored the brain activity of over 120 volunteers. Age between 4 and 40. Even though they weren't looking for it, they couldn't help but notice the differences of brain activities of between the boys and girls in the tween and teenage groups.