Generally a juvenile matter is not considered a criminal conviction so you would not have to disclose it on an application. However, some job types are more sensitive than other. For instance, a law enforcement application requires that much more be disclosed than your typical job.
Regardless, I would look into sealing your juvenile record. Your juvenile records do appear on your criminal record. Upon your 18th birthday, you are eligible to petition to have your juvenile records sealed. Once sealed, no one can gain access to them and they will be completely destroyed five years from the date of sealing.
Juvenile records are not automatically sealed upon your 18th birthday. You must affirmatively petition the juvenile court to have them sealed.
If you were convicted as a juvenile and you were not sent to the California Youth Authority, you can serve a petition on the court to seal and destroy the records of your conviction. Once the petition is granted, the records of your arrest that are in the custody of the juvenile court, the probation officer and any other agency, including law enforcement agencies and public officials, will be sealed and later destroyed.
Once the record is sealed, the proceedings in your case shall be deemed never to have occurred and you can deny ever having had the conviction.
Although a juvenile case is not considered a "conviction" if you were charged with a DUI as an adult, it can still appear on your DMV record.
You should do two things. You should get an H6 printout from DMV. This should confirm whether or not the DUI appears on your record. If it was a true diverson, it should not appear on the complete DMV record. Secondly, as suggested earlier, you should check your juvenile record and consider having it sealed.
Note, however, if the DUI shows up on DMV, that will remain there, even if you have your record sealed. This is regardless of the 7 or 10 year time limits that you discuss.
Juvenile matters do not constitute crimes as such. Moreover you could have had your juvenile records sealed at 18. Having said that there would still be a DMV record of your DUI which is separate from the criminal prosecution. Your employer could easily find out if he wanted to. IMHO the best strategy is to tell the truth with an explanation because otherwise the employer may feel that you lied on your application even if you are technically correct about not having a conviction.