On this one I agree with
@Logiko @Chrono
Who are we to judge a multi millenial culture ?
Today the west dictates their will because they are the strongest (the strongest always decide who does what) but the west is in a huge decline and soon the rules will change and so on.
Most cultures up until the 20th century considered a girl a woman when she starts getting her periods and the boys become men when they can ejaculate; everything is tied to procreation which is fair since this is how nature works.
''Teenager'' is a 20th century creation and never existed before, you go from child to adult without transition which again is fair.