Yes, so very mature. I'd definitely call a character mature if their brother sacrificed his existence to make him powerful and eventually go to the Leaf village in peace, and the person just completely disregarded his wishes. And of course, it's completely fine to waste your newfound power on basically harmless Zetsus. Oh yes, and let's not forget that he went to Orochimaru and basically said, "Naruto and Konoha, I hate you and I'm gonna disregard everything you've done for me because I'm a teenager who's soooo frigging misunderstood." Yes, this is the epitome of mature.