Honestly, the guy is playing up for the sympathy vote.
He's claiming he's not mentally capable. Aspergers or not he hacked into The Pentagon, The Pentagon. That's not really something you can do by accident, he knew what he was doing, he thought he could get away with it.
Unsurprisingly the Americans have come down on him like a ton of bricks, I don't think he should get 60years but he should stand trial just like anyone else, since his offences were targetted against the US government that's where he stands trial.
Incidentally the penalty for stealing/attempting to steal military secrets in the UK is life.