Maybe, but otherwise that does sound a tad condescending to twelve year olds. You do realize that he can read what we're saying right? Saying "He only did that because he's twelve" might look to us like giving him the benefit of the doubt for doing something that would otherwise be seen as annoying and a bit embarrassing for him, but to a twelve year old I'm guessing it probably looks more like "hey look at this silly immature thing that kid did it's so typical for his age let's all share in a benevolent eye roll and a good hearted laugh." Of course I could be wrong, it's just how I probably felt about it when people said things like that when I was twelve.
Do most twelve year olds shout that often? I'm pretty sure that most of the times I've shouted in my life have been because of anxiety attacks, not excitement. Excitement alone might often have made me too loud, but not enough to type in all caps for a whole paragraph. Then again I have written some VERY long and overly enthusiastic reviews for online novels I've liked, but I only stopped doing that in the past couple years...
