You can stay 15 forever while the rest of us grow up and our musical tastes evolve. Out of any band that came up during that neon pop rock movement The Maine has the most of my respect in how they've evolved musically and as people in general.
Just because someone likes a band's older material doesn't make them immature. In my opinion, The Maine was way better during the CSWS era. The music they make now is boring as hell. Look at All Time Low. They never strayed from pop-punk. Since I still listen to them, does that mean I haven't grown up?