So, it seems like only the lines "last Christmas" and "twelve" make this so very chan, and it really doesn't read like he has to be from the rest of the story. Other than that, I like this, but the extra-chan is a bit tricky for me. I'll admit the AU made me rather expect Harry to be a bit older, since it's usually later canon people want to dodge. If Harry'd been fifteen or a bit older but still underage, I'd be unconditionally cheering on the story :).