Given the way the 18th birthday was emphasized, it was probably relevant for criminally culpabilty. It is possible that 17-14 is not prosecutable because of the structure of the Romeo and Juliet law or it may be that 18 is the point that one can be charged as an adult and face harsher consequnces. Nevertheless, they found out about the sexual relatuoinship and did not control their daughter enough to stop it.