What is the moral high ground for the age of consent? You haven't answered that yet.
Science tells us that the physical laws of nature existed before space and time existed. Likewise moral laws would have also existed for the same reason. All laws of nature were in place before space and time. Science, music, mathematics and the laws of nature were waiting in eternity to be discovered. Everything which has happened since space and time were created has happened because of the laws of nature. In effect everything which exists has been pre-ordained.
The highest standard for the age of consent is that there is not one age but a right age for each young adult. This would apply for two young adults of the approximate same age. If that is not good enough for you, then use 18. There will never be a right age of consent for a full grown adult to take advantage of a young adult. But if that is not good enough for you then use 21.
Men know right from wrong. You cannot write enough laws to capture right and wrong. You should not even try because then you will get assholes like you who will never hold themselves to a higher standard. This is called legal positivism and leads to the kind of society we have today. So instead of people erring on the side of right with their conduct, they do as you do and only follow the letter of the law which will always have loopholes and inconsistencies.