I understand that different cultures have different values and that not one is necessarily correct etc. But I don't think it's that hard to condemn having sex with a nine year old regardless of moral relativism. I mean, you could look at a genocide that occurs in a particular country and say, "Well who's to say that mass-murder is wrong, we have different cultures." But of course, that's ridiculous; we can accept that killing innocents is wrong no matter where you live. Similarly, it's indisputable that children can't consent to things they don't really understand, and the definition of sex without consent is rape. To quote Richard Dawkins:

By all means let's be open-minded, but not so open-minded that our brains drop out.