Well, you're getting the underlying concept wrong. It's about the question "who is it to decide if a child is mature enough, the parents or the state?" Most European countries answer this question with "the parents". So they allow a relatively young age of consent but allow parents to intervene if they think it's needed. You get in legal troubles if you fuck a 14 years old girl (or boy) when her parents disagree because they think she's too immature. The idea is to allow sex for the younger, early matured people but still have an opportunity to punish people that abuse immatureness.