Ok, I’m not entirely sure what you’re arguing for then. Are you saying the age of consent should be raised to 18 universally? Or maybe that there should be more laws restricting the ‘age gap’ between sexual partners?
I understand that you have a personal aversion to sexual intercourse between two individuals with a large age gap. It seems to me though that any two (or more) individuals that meet the standard of informed consent should be permitted to have sex. The brain (at least in men) does not stop developing until around 25. I think ‘a fully developed brain’ is a poor standard for determining whether a person can give informed consent.