New Jersey Underage DUI
If you are under the legal drinking age of 21, you can be charged with Driving Under the Influence if you have ANY alcohol in your system. Even if it seems like you are okay to drive, this does not matter. If your BAC is .01 or higher, you will face a 30-90 day suspension of your driving privilege. You will also have to perform 15-30 days community service, and attend the Intoxicated Drivers' Resource Center.
Also, even a person under the age of 21 can be convicted of a "regular" DUI. If you are intoxicated enough to not pass field sobriety tests and can be convicted on observations alone, or if your BAC is .08 or above, you will face the same penalties as a person of legal drinking age. Those penalties are severe, as indicated in all of my other posts on this site.
You absolutely should not drink under age, and if you do, under no circumstances should you operate a motor vehicle. Whether you believe you are intoxicated is irrelevant, as the bar for conviction of an underage DUI is set incredibly low.