Gabu et al,
I don't believe that curfews are in place because of violence, necessarily, just criminal behavior in general. And though perhaps it's true that teenagers have no natural inclination towards
violence specifically, it is true that we are more likely to make irrational and/or unplanned actions. This is because our frontal lobes (the part of the brain that plans and coordinates behavior) are less developed, meaning we are less likely to reason out our actions and will instead depend more on the more developed regions of our brain, such as emotional centers and the like. Though not inherently criminal or violent, it's easy to see how doing such things could translate into criminal or violent behavior; whereas an adult might think about the consequences of his actions before, say, keying an enemy's car or getting involved in a nasty fight, teenagers will be more likely to live in the moment.
The
Sydney Morning Herald had an article about this, the
Boston Globe's article on a local seminar has some more information, and of course
Wikipedia is always your friend.
I'm surprised no one else brought this up.