What part of the song do you find immature?
I personally like the music, but I really hate the whole heartbroken girlfriend killer lyrics. It's not like he has 10 girls in his basement, so don't sing about it, it also isn't metaphorical so yeah. Just leave it out please.
Although, the music itself got worse, the lyrics are 10x better in latter stuff. One of my fave lyricists to date because of it