There is always the possibility that english isn't his first langauge. In that case he is making an effort to communicate in the same language as everyone else here. For that you could give him some slack and some credit, of course if that is the case he should probably mention it somewhere.

"If he's unwilling to learn to do that, there's no reason to treat him like an adult." First offenses merrit a little more lee way han this just to be polite. Any 6 year old could tell you that. Politness is a skill my 2.5 year old has mastered so why can't you? Perhaps you arn't as smart as her?