No, your record does not automatically clear when you turn 18. You should contact a local attorney to discuss sealing your juvenile record.
The information provided in this answer does not create an attorney-client relationship and is not considered to be legal advice.
No, you have to affirmatively do something to have records sealed or expunged, in most cases
No legal advice is given here. My responses to questions on Avvo are never intended as legal advice and must NOT be relied upon as if they were legal advice. I give legal advice ONLY in the course of a formal attorney-client relationship. Exchange of information through Avvo's Questions & Answers forum does not establish an attorney-client relationship with me. That relationship is established only by joint execution of a written agreement for legal services. I am only licensed in the States of California and New York and the District of Columbia
Unfortunately, in the digital age your criminal record remains with you forever. To some degree or another this is true regardless of whether your ultimately seal or expunge a case. All arrests are natters of public record, and, even if removed from the public record they remain in private records This is one down-side to technology.
As for sealing / expunging, again, I suspect that it doesn't much matter where you were arrested, what you were arrested for, what the final disposition was or whether or not you sealed / expunged the record. This is 2014 and we are forehead deep into the internet age, where nothing is private, sacred or truly hidden from public scrutiny.
Sadly, sealing (and expunging) only applies to certain (not even to all) government agencies and has no effect whatsoever on private (er, extortionist) enterprise, who compile and maintain arrest information and then demand that you pay them off to remove your information from their database and public access. Worse still, after you "buy back your information", then you can count on there being another private company lurking, somewhere, sometime, somehow, just waiting for you to pay them off as well. Its a seemingly never-ending vicious cycle.
For better or for worse you are probably best advised to take the wind out of the sails by admitting your past issues / indiscretions to your present (or potential) employer, lender, landlord, etcetera, rather than waiting for them to find out on their own.
I hope that this has been helpful.
First, second and third: No attorney-client relationship exists by virtue of any Q&A with Michael A. Haber, Esq. on Avvo. Fourth: Anything that you post on Avvo (or on similar sites) or on any social media is by its nature public. It is essentially an admission / confession and can be introduced into evidence as a statement against your interest in a subsequent legal proceeding. Once posted you lose any reasonable expectation of privacy, so, as this is an open forum (with no privilege attached), please be extra careful when considering what to post online (forewarned is forearmed.)