From The L.A. Times: Rivers Cuomo has no problem admitting that he sometimes still feels like a teenager. "Maybe I haven't matured in some ways that other 40-year-olds have," the Weezer frontman said in a recent interview. "Or maybe I'm more willing to honor those immature voices inside myself that other 40-year-olds aren't."He certainly isn't very age-appropriate when performing, which is a goo…