Flank Attack Defeated by Central Play

A game I have recently played here. My opponent's plays aggressively in the beginning, but ends up in trouble when his king is left in the center.

 Ah! I didn't notice that. Thank you for pointing that out. I fixed it and also some other minor errors. 

 He is not, in fact, he is a rather strong player. He simply underestimated me this game (I'm about 100 points higher now), and we played another after, which turned into a hard fought draw. As Jstrong said, the knight was pinned to the king, and, besides, Why would an NM comment on a missed mate in two but then neglect to say my opponent could have gobbled up my queen!? 

You really should finish the game.  I don't see a mate coming?

 The game is finished, he resigned. To be down a rook down in a much inferior position is reason enough to resign.

Your assessment of Black's 6th move was dead on correct. The game would have been completely different had he simply developed where he could and castled, and allowed you to commit your king to one side or the other BEFORE pushing flank pawns.

You are correct in saying that you were underestimated. My motto is "Pay no attention to anyone's rating. Experience and study trumps ratings." And experience, not just on a particular site, but throughout a player's chess life is not revealed on a profile. At the time of this posting I have only completed 10 or 11 games. How would anyone know that I've been playing chess for 30 years? In a blitz game, I defeated an opponent with Boden's mate. I saw the mate several moves before it happenned. Why? Study. These things are not revealed on any profile.

My point is this: assume every opponent is a grand master and remember the object of the game - checkmate!