A person who was convicted of a San Diego DUI while a minor will be only be charged in court for a “first offense DUI” upon being arrested for a new DUI.
The difference between a first offense DUI and a second offense DUI means substantially increased punishment – see San Diego California DUI Penalties here.
Unfortunately, California DMV will treat him as an enhanced second offender, will impose multiple DUI offender length of suspension periods, e.g. upon upholding an administrative license action, and may require a multiple offender alcohol program if convicted.
A finding that a juvenile has committed an offense is equivalent to a conviction of a violation of the same offense, but only for the purpose of the DMV’s driving privilege suspension and revocation provisions of California Vehicle Code Sections 13100 et seq. [See California Vehicle Code sections 13105, 13352(a) and (b), and 13352.2.]
Past minor adjudications cannot be charged as sentence enhancement in California DUI cases and the court cannot consider them at sentencing for a later adult DUI offense. [California Welfare & Institutions Code section 203; People v. Bernard (1988) 204 Cal.App.3d Supp. 16]
Juvenile traffic court records are destroyed, but may be microfilmed, after 5 years or at age 21. [ Welf. & Inst. C. section 826]
An effective & preemptive San Diego DUI Criminal Defense Lawyer tactic can be to have the juvenile finding sealed and destroyed on petition to the Juvenile Probation Department, and to have the JPD submit a copy of that action to DMV.
Otherwise, DMV is permitted under California Vehicle Code Section 13105 to act on juvenile “convictions,” but such convictions may not be pled, proved or considered by a California DUI court in connection with any subsequent DUI offense.
CVC 13352(b) provides that for purposes of CVC 13352(a)(2) through (a)(9), the multiple DUI offender license suspension and revocation provisions, a juvenile finding of a DUI or drunk driving violation is a “conviction.”
This is a relatively complicated area of California DUI law. All such arrestees are urged to immediately consult with a recognized San Diego California DUI Attorney Specialist.
See also this Yahoo answer.