I've always been really interested in characters that are 'aged beyond their years', but not 'wise' beyond their years. For example, the world my story is set in is incredibly violent and more or less devoid of innocence, and has a life expectancy similar to that of early industrial societies. Not because of a high infant mortality rate, but because the demographic of young males is over represented, and it's fairly normal for people to be armed in their day-to-day lives. None of the male characters in my story are older than 20, but they're technically fully functional adults, despite the fact that they've yet to develop any real sense of morals, or even a basic understanding of the difference between right and wrong.
I've been trying to make a nice contrast between the characters' mental maturity and emotional immaturity, but I find that I can't come up with an elegant way to do it. The best thing I've been able to come up with is to contrast the intense violence they take part in every day with a fratboyish social life. But I want to find a way to portray them as children from an emotional standpoint. I was hoping for some suggestions.