I'm one of those who just can't believe that a 12-15 year old is mentally or emotionally capable of assuming
the sort of leadership position you outline.
If the race is human, then I cannot forget the fact that the human brain is still being formed until 18+ years.
And although I think I've meant some remarkable young people - someone capable of commanding a small military unit? Yeah, well...
Then perhaps you should stop relying on what you can or cannot believe as a means to form opinions?
The fact that the human brain keeps on developing for a long time, does not mean that mental and emotional
maturity of people who've yet to pass the peak of brain development is necessarily lower than those
who've passed it.
This is highly individual, and has a lot more to do with indvidual experiences and environmental pressures
than with the average facts of human biology at the level of the brain.
I know plenty of people my age (round 30) who're less emotionally stable and developed than I was back in High school
for christs sake, because they've grown up in sheltered enviroments that enable and indulge
their emotional frailty and mental incompetence.
Secondly, the rather ignorant idea that seem to be so common in todays society of treating people under 18 as children,
is a very modern trend that was not at all common in pre-industrial societies, where you do in fact find
people in the 15-25 range being given responsiblities and roles we today wouldn't dream of giving to people under 20-35
in most developed countries today.
People in general grow on adversity and responsibility. Young people are no exception. Sure, some people drown in it,
but many don't - and to think that people in their late teens or early twenties can't hack it in the roles
attributed to them in most fantasy narratives, ignores the majority of human history (where people in those age
groups were forces to farm, fight in wars, etc.), ignores the plasticity of the human brain and its ability
to adapt, and ignores the patently obvious fact that these are fantastical narratives that tell stories about,
supposedly, the best mankind has to offer - not your average "oh high school was
so hard, I think I have PTSD because dad didn't buy me a car for my 16th birthday"-U.S youngsters.
Not saying that it isn't more reasonable to imagine leaders of warbands to be past their mid-twenties -
simply saying that the world isn't always so conventient, and that making a younger than average party
for the roles they inhabit is not something that should break immersion any more than any of the other
fantastical hallmarks of fantasy story-telling if you're going to be consistent about your attitudes.