If you weren’t convinced by his deepening voice, consider this latest milestone on Justin Bieber’s road to maturity: According to Star magazine, a 20-year-old California woman is claiming that Bieber is the father of her new child. The court documents allege that she and 17-year-old Justin had sex backstage at one of his concerts, and that she’s asking for a paternity test, plus paternal support should Biebz turn out to be the father. Given the source, his camp’s denials, plus the fact that Justin Bieber is the most closely managed pop star in the Western hemisphere and probably wouldn’t get to hang around alone with an older woman in his dressing room, this is almost surely untrue, but still: Welcome to adulthood, Justin Bieber! That happened so fast. [Page Six/NYP]