Under the state’s zero-tolerance law, it’s illegal to be in physical control of a vehicle with any measurable amount of alcohol in your system if you are under 21 years of age (even if you are 18 or older, making you legally an adult). The legal limit of 0.01% BAC reflects this strict rule. Driving after just one drink, if you’re below the age of 21, may put you at risk of being charged with an underage DUI violation.