Mary-Kate Olsen

When Mary-Kate and her twin sister Ashley were cast as one character on the family sitcom Full House at the age of nine months in 1987, no one could have predicted that they would soon rule a billion-dollar entertainment empire. After releasing an album and filming a TV-movie in 1992, the duo formed the production company Dualstar, making them the youngest producers in history. Throughout the '90s and early '00s, the Olsens made a plethora of direct-to-video movies, a handful of features, starred in a number of series, released albums, published a magazine and even launched a clothing line, making them unmistakable pop-culture icons. Although their success was thanks in large part to their status as twins, as the sisters grew up they understandably tried to forge their own identities. They sported different outfits and hairstyles, and Mary-Kate seemed to be the rebel while Ashley embraced a primmer persona. In 2004, they turned 18, released their first major Hollywood picture, New York Minute (it bombed) and took time off from their busy careers to enroll at New York University. Mary-Kate also entered rehab to seek treatment for an eating disorder. While the Olsens are certainly all grown up, it remains unclear whether they will be able to make the leap to adulthood onscreen.