[quote=@Fabricant451]
<Snipped quote by IncredibleBee>


I mean, a 22 year old person is probably more likely to be studied at a university rather than a high school. 
[/quote]

I was expecting you to say that.
Being 22 doesn't matter. Kodor has no formal education and speaks only a little English. Or I guess technically Japanese, but we write it as English, because that's our common language.

Secondly, the magical schools that exist seem to be rather secretive. This means that one building is going to house a larger portion of the magical society, so this school could actually encompass high school, but also middle school and even university ages.
But what's more important than Kodor's education is Kodor's use FOR education. As I said previously, psychologists and sociologists would have a field day with someone like him. So while he's learning things like reading, 'riting, and 'rithmitic, he's also learning to integrate with society and in the future he'll be useful as a guide in his homeland, a dangerous wasteland filled with rare and dangerous things.

One might say his existence at the school is a little odd, but the school teaches wizards and demons. If half your student body is pyromancers, Kodor's almost normal for you.