Federal law makes it criminal to engage in a sexual act with another person who is between the age of 12 and 16 if they are at least four years younger than you. Each state takes a different approach as the age of consent has ranged from 10 to 18. For example, a state might set the age of consent at 18.

Is it illegal to date someone 18 when your 15?

The law criminalises people who have sex with under-16-year-olds. So, if an 18-year-old is having consensual sex with a 15-year-old, the 18-year-old is guilty of an offence and the 15-year-old is the victim. The law gets confusing (and unworkable) where both partners are under 16.