Riding the planet around the sun a certain number of times does not make one a competent adult in and of itself. However, if you're looking for sex with someone under 18-ish, I'll still look askance at you, law or no law. And if the State demands that you be treated as an incompetent when you have demonstrated you are competent, I would prefer to treat you as competent.

Government is just a group of power-hungry sociopaths who want control, and no "protect the children" excuses can conceal that from honest inquiry.