I'd say the average 12-13 year old could comfortably pass N1; that said, the average 12-13 year old is fluent in Japanese. Not getting 100% of course... but you

I'd say the average 12-13 year old could comfortably pass N1; that said, the average 12-13 year old is fluent in Japanese. Not getting 100% of course... but you don't need 100% knowledge of a language to be fluent and communicate on an everyday basis. With N3 you might be able to introduce yourself and have a very basic conversation. I think different people have very working definitions of fluency.