Currently, it is perfectly legal for any non-minor to have sex with a minor that is of the age of consent for that state. That means that an 80 year old man could have sex with a 15 year old girl if 15 is the age of consent for the state.
The age of consent was most likely lowered in most states to allow teens to be teens and not be arrested for having sex with someone their own age. It was not intended to let old perverts have their way with high school students.
The age of consent in some states can make it difficult for parents to protect their own children since police will say that there is nothing they can do because a child is of the age of consent. They could only tell the parents to file a restraining order. This law should help protect the rights of the parents.