If you were age 19, you would not be a minor.

Airlines often run background checks AFTER you show up for class (not sure how that might work for interns). They don't want to spend the money until you show up (not everyone shows up for new hire class). They can always fire you during training if anything comes up on the background check...but they should give you the opportunity to disclose during the interview process.

In the case of an intern, I suspect they would be looking at SIDA access to airport secure areas and insurance requirements for driving company vehicles. You will have no problem with SIDA access, not sure if insurance could be a problem with no conviction (I doubt it).

If you feel the need to be less-than-honest, better talk to a labor lawyer and find out if they can hold it against you. Generally, I would say be honest. It might cost you a job offer, but that is better than getting caught lying and getting fired. You were young when it happened...as time passes it will be less of an issue.