Being in the wrong place at the wrong time can last a lifetime. Records of conviction for misdemeanor and felony offenses do not expire or evaporate, nor can they be completely erased.
Types of Records
Juvenile records -- convictions prior to age 18 -- are "sealed," meaning that they will not appear in most background checks and need not be revealed to prospective employers. If an individual is arrested and charges are dismissed, greatly reduced or result in a verdict of not guilty, he can ask that the court seal the record. Both types of records will still be available to law enforcement.
It is illegal for prospective employers to discriminate on the basis of past convictions that have no bearing on the job in question. In reality, it is extremely difficult to prove this type of discrimination and rare for a job seeker to be interviewed after answering "yes" to the conviction question.
Most states offer some type of relief from the disability of a past conviction. It may be called expungement or a certificate of good conduct. The program is often administered through a state's Department of Corrections or state-level court system.