Heheh... Undead thread walking.
As far as PCs, simply being very young, go, I believe I'm with B on the "hey, why not?" position.
In icelandic sagas and danish chronicles of the time of the sword, it is not unheard of with wild kids the age of 10 to kill grown warriors for the first time, and continue on amazing sprees of violence up until early adulthood when the other kids go on their first raids...
Of course, today, they would be soooo in for guidance councilling, BIG time.... Which is no doubt a good thing. But still, who'd wanna roleplay through modern day wussiness and bureaucracy in their spare time? Your GM would have to be one hardcore standup comedian to make the sessions halfway entertaining, I think.
On the other hand, I still think the PCs sexual development should be postponed and tuned down as much as possible, even in the case of adult PCs. Basically, because there is no reason for it not to be, that I can think of, which isn't somewhat contrary to having roleplaying fun, and more about trying to import your lovelife into the game, where it doesn't help or improve anything. Sex and sexual innuendo in rp might have its place, just like diarrhoea; but on a general note, I think it doesn't really belong.
But violence... as we all know(?) the joy of violence is more of a mental powerrush than a physical one, where it is rather exhausting, unless you are a natural berserker, in which case you probably need to rp less, and visit your guidance councillor more...