my understanding is, there are different rules in different states. in new york they lowered the age of consent from 18 to 17. in new jersey they lowered it to 13(?). in some states, while the age of consent is fixed at 18, exceptions might be made considering the age of the accused. for example, minor is 16 while adult is 19. since there is less than four year gap in age, no crime. while if the adult was 21, then it would be a crime as age difference is greater than four years.