Any sexual activity with a person under 18, even if both are under 18, is illegal. There is no exception for sexual relationships hat began before one of the parties was 18. Its still illegal

What happens if two people are dating and one turns 18?

Statutory Rape (California Penal Code Section 261.5) Under California Penal Code Section 261.5, it is a crime for any person to have sexual intercourse with any other person who is both under the age of 18 and who is not the spouse of the person accused of the crime.

Is it illegal to date someone under the age of 18 when you are 18?

There arent any laws around being in a non-sexual relationship where one person is under 18 and the other over. Once you turn 16 its not illegal for someone to have sex with you no matter how old they are.