It depends on the specific offense the prosecutor files against the underage driver. Civil offenses will not count as priors because they do not meet the same requirements as a criminal DUI offense.
However, underage drivers can still be charged with DUI when their blood alcohol concentration is 0.08 percent or higher. This criminal offense can be alleged as a “prior” in future DUI cases for enhanced DUI sentencing - but only if the driver was not a minor at the time of the conviction.
Drivers under the age of 18 can only face adult charges for serious criminal offenses. DUIs do not qualify, so the case remains in juvenile court. The case becomes an adjudication, not a conviction, and thus cannot be a prior in future adult DUI cases. These rules are complicated. Get a defense lawyer on your side in any DUI case to prevent an underage DUI from being unfairly alleged as a prior.