Penalties have crept up. If you were convicted of drunk driving in Massachusetts in 1993, you are not disqualified from having a gun. If you were convicted of the same crime in 1994 you are disqualified. A criminal conviction remains forever unless you are pardoned, have the record expunged or you live in a state that automatically expunges a record on the passage of time. Most states do not automatically expunge records.
Some states seal records after a period of time.
The sealing of a record does not remove the conviction, it simply hides it from the general public. If you have a sealed record, you should consult with your attorney before answering any governmental questionnaire that asks about convictions. In my client's case, if he had a conviction, even though it was over 35 years ago, it was still a conviction. With improvements in data entry and computers, you cannot assume that old records will not be found. This brings us back to my client.