If you are under 21, you have to blow a 0.0 whether you are driving, walking, whatever. Over 21 i'm almost positive you can blow under a .08 and be fine.
still officer discression. if i pop 2 painkillers and have a beer then im probably going to be buzzed and still blow below the legal limit. thats what the field sobriety test is for. but yea, if he was under 21. anything over a .00 is grounds for a DUI.