Many jurisdictions have a certain set period of time in which misdemeanor charges and/or traffic violations purged from the records. Which means, by law, they no longer have to keep them. Although I can not speak for your jurisdiction, that time period could be up to 9 years depending on severity of that particular charge/violation and local statutes.
If you can imagine, courts view misdemeanor and/or traffic records somewhat like your credit score. After a while you're sort of "forgiven", but that doesn't mean it goes away. Arrest records are separate from the court records. Court records are public documents. Anyone, let's say a potential employer, who wants a copy generally pays a fee, and gets and exact copy. Minus any personal information like addresses, phone numbers, names of witnesses and names of juveniles. These things are generally blacked out.
Arrest records on the other hand, are records kept by law enforcement agencies. So every time they run your license or license plates on your car, they know what crimes you've committed, regardless of whether or not they've been purged from public court records. I should note, arrest records are not generally available to the public. Also, I think you should know that your fingerprints were more than likely entered into a database. So (trying not to be suggestive, as I don't know you) IF law enforcement came across a situation evolving your finger prints at a later date, you may be easily identified.
Rules for Juveniles are a little different though. Juvenile records are generally sealed or expunged upon that juveniles 18th or 21st birthday depending on the jurisdiction and/or court requirements. I suggest calling your County Clerk of Courts Office and ask them.