Not even close. Regardless of what a minor thinks about their dating situation, they are not legally capable of giving consent. And California law is VERY clear that the age of consent is 18 - so IF there is something going on, it is most certainly enforceable.
By that logic, don't bother to arrest that crack dealer over there, because he's only got two more rocks on him and once those are sold he'll be done with criminal activity for the night.If they are doing something illegal, it's not going to be illegal for much longer since she will be 18 soon enough.

