I don’t know the law in all 50 states but I’m licensed to practice in two of them. The age difference is not a factor in either of them as long as one party is at least 16. The 4 year rule you’re referring to applies to situations where one of the parties is at least 12 but younger than 16. So a 20 year old engaging with a 13 year old is illegal. But a 17 year old with the same 13 year old is not (depending on birthdays). Pretty messed up.
45 years ago my lawyer told me” make them swear on a Bible on court snd men will break and tell the truth but women will lie ..”