[Crazy Jetty]

He's a kid. I can see him getting really excited and annoying everyone when he;s on the shield carrier. I can see him going fanboy when he meets his own heroes, like Tony Stark.
But I definately agree with the general lack of responcibility he has. Out in battle, he should be way more concerned with what's going on than he is. Now, he's too concerned with showing off, and showing up Nova.
While I do not like the other teenagers chosen (I agree that Torch, Iceman, and Kitty would have been way better. With all the marvel teenagers who get so little exposure, why shoehorn adults into this role instead?), the whole group dynamic would work so much better had they stayed true to his personality in the Ultimate comic.

This really is Spiderman: The Sitcom. Especially with Shield taking over his school life.