[Something's wrong. He can tell by the way she's looking at him with her brows lifted and a frown on her face. Dean weighs his options. Sure, he could ask, but that might open the flood gates for a conversation he doesn't want to have.]

Usually? 12 years. Not counting college. You can drop out and get a GED but I'm not sure that applies to Asgard. It's not your typical school. It teaches subjects that aren't really on the roster in real-time.