First of all, I'm pretty sure that a minor who engages in acts of sex is committing no crime. There's likely no law: "You must be 14 years of age to have sexual intercourse and must be 18 years of age to engage in deviant acts of sex."
A different issue is statutory rape. The basic age of consent in NY is 17. That means that someone 18+ is guilty of statutory rape if they have consensual sex with someone 16 or younger. But the 16 year old is guilty of no crime by virtue of being 16 and having sex.
That means 18 and 17 is OK. I'm not sure what happens if both are 16 and under.