Even though she was 26, McAdams totally ruled in 2004’s Mean Girls as Regina George, the ruthless leader of the cool girls clique at North Shore High School. Oddly enough, she also looked just as young as her costar Lindsay Lohan, who actually was a teen at the time! Now 42, the actress has since graduated to grade-A, grown-up roles in films like 2015’s Spotlight, for which she nabbed an Oscar nod.