I have no f---in idea.
Ichigo from Bleach is only fifthteen, and there are others too. The girl with the huge boobs, Orihime, only 15... LOL.
Damn these "kids" are younger than me... but they look like full grown adults. It's sorta an Anime cliche that most main characters (from Shounen I mean) are below 17 years old with at least one dead parent, or it's unknown throughout the story. Or teens hoppin in a huge robot and havin full control from the start and knowin how to pilot it...
Overall it's aimed at a certain age of audience, in the same way that Shounen is aimmed at guys but then they add some aspect to the Shounen so they can get girls to watch it too.
Yu Yu Hakusho rocks... to bad I missed the last round of fights in the Dark Tournament (except Yusuke vs Younger Toguro). Then I missed every episode after that one guy used his sacred power, because the time Yu Yu Hakusho came on suddenly changed to 5:00 in the morning. I had missed so many episodes better believe I was pissed.