besides, most of the time, genins won't get into mission that involve serious fighting and killing, the best they get is a bunch of bandits once in a while...

they become chunin at age 15 or something (most of them, regard this years exam and some super geniouses) and only then they get the chance to kill someone, so it's really not that diffrenett from being raised in a samurai family or living in a military boarding school.