Mary-Kate and Ashley Olsen turned 21 Thursday, a milestone birthday for the famous former child stars. Though they still have a huge fan base, much of it springing from the tween and teen set (not to mention a host of men who just love the way they look), the well-known identical twins have been seen less and less in movies and TV and more and more in tabloids. Are they quickly heading down a darkened path of former child stardom, the road many other actors have trod? Not every child actor fades into obscurity – just look at former wild child Drew Barrymore, who was famous tabloid fodder for drug abuse problems and a score of other antics when she was 19. Today, Barrymore is one of Hollywood’s more bankable stars. Or will Mary-Kate and Ashley end up like the Gabor sisters twenty years from now – older, famous, and still sisters, but no one can remember how they got famous in the first place?