I don't know about being under 21. But back in January when my mom brought a gun from Kalifornia to give to me she didn't need to be present even though she was. Just make sure you don't go through the second set of doors with it. They get real upset. Make sure the weapon is clear before going in and there is small rotating window after the first set of doors.
And I think it might need to be in your name when carrying. But let me state the standard I AM NOT A LAWYER.