Verified answer

Not mature..

It's not mature as in R-rated. It deals with relationship issues, so it covers somewhat mature topics. But I don't recall any nudity or much fanservice. It's a romantic comedy.

I would think that a youngster might find the subject matter boring because it goes over their heads, more than it would be inappropriate.

It's not mature. It's a good PG13 anime (PG13 is the official US rating for it). There's no nudity or gore or highly suggestive parts. There's a bit of fighting but nothing overly violent. I don't see why it would be classified as "mature".