It depends on which state he lives in. I don't know about NJ.
If the minimum age of consent in NJ is 16 or less (though I think 16 is the lowest age of consent in the U.S.), then any sex act between these two boys would be a crime in which the younger boy is the victim. The crime would be statutory rape.
If the age of consent is greater than 16, it would still be illegal, but the crime would be different. I'm not sure what it would be. The older boy would probably get hit with some coercion charge or something, though. The younger could get off scot-free in the end.
I'm no legal expert, far from it, so I could be wrong about that stuff. I have taken law classes though, which is what I based all of this on.