Whether or not you as a convicted juvenile can possess a firearm legally even where your criminal file is sealed depends upon many factors under the law of your state. Some convicted felons who are on parole or probation cannot have a firearm in their possession.Some states allow juveniles convicted of a felony who are now adults to have a firearm in their possession. Most likely the answer to your question is that you can, however the caveat is that you have not written what state you were convicted of a felony in and what state you currently reside in.