The legal age in Maine is "18" folks. 18!
Very clear. Then age was NOT an issue. Then does this smoke shop consider Military ID unacceptable? That question has yet to be answered. If, and I stress if, this young man was denied service because he was in the military, FR should come down on him like a ton of bricks. However, in a heavily-regulated state like Maine, the owner may have doing some serious 'CYA', fearing a possible sting. We need more details.