In Texas the difference between DWI and DUI comes down to the age of the defendant. Driving Under the Influence of Alcohol (DUI) refers to a minor. If you are under the age of 21 and suspected of driving with any detectable amount of alcohol in your system you could be charged with DUI. You do not have to be intoxicated to be charged with DUI minor. The State only need show a person under the age of 21 has a detectable amount of alcohol in their system. However, if you are a minor and intoxicated the State can and will still charge you with DWI.
DUI minor is governed by the Alcoholic Beverage Code instead of the Texas Penal Code like DWI. A conviction for DUI minor is punishable by a fine only (no jail time) and a license suspension. Unlike a conviction for DWI you can can get the case expunged if you can reach the age of 21 without any more convictions under the Alcoholic Beverage Code.