I guess you would give your kids consent at early age without teaching them that there are percussions for their actions.
What would I do?
I would teach them about love at an early age. when they get to the age of 15, i'll sit them down and tell them it's ok, as long as they're doing it safely. i'd even let them do it in my house.
that way, i know they're in a safe environment, having safe love, and that they know they can come to me with any problems. liberal i know, but better than your "sticking head in the sand" method.
The +18 part is a reference to the US law where it says you can't give consent. Like my Criminal Justice teacher said, "Your parents can't give consent, but if you are going to have love atleast wear a condom."
my point still stands. your idea of parenting when it comes to love is the definition of ignorance. teenagers are going to have love, whether you like it or not. better you allow it and have some control than disallow and have none.