I don't know why some people think he should be given a break just because he's a teenager. I've known teenagers who were late for work and were then rude and arrogant about it. They got sacked.
Most people don't make excuses for teenagers if they are unpleasant. Just as we wouldn't for adults who were similarly unpleasant. Making excuses for them and allowing them to play the victim is why they carry on being dicks well into adulthood.
If he's acting a cock, he should be called on it. Being young is no excuse. He should be grateful he's not in the position most 19-year-olds are. If he acted the way he does then, he'd be lucky to be flipping burgers in McDonalds.