I'm afraid this topic has wandered into an area that is less about what consent is or isn't and more into kiddie diddling. I'm not here to defend that, never have, never will, despite the attempts of the resident Prohibitionist to shackle me to his own demons.
Anyhow, the object of a law shouldn't be to penalize consensual activity, it should be to protect people from non consensual forcible activity, when it can be proven that is what occurred. You don't protect anyone when you take away their right of self determination and replace it with a standard you have already admitted is arbitrary or contradictory though.
Simply by making a law facts do not change to conform to the law. The law is either in agreement with natural law or not. If a person HAS the wherewithal to consent, preventing them from doing so then becomes the forcible act and not the act of protecting that it purports to be.