(contactmusic.com) - Playboy boss Hugh Hefner is hoping to convince the Olsen twins to celebrate their 22nd birthday in June (08) by stripping off in the magazine. The media mogul has attempted to woo Mary-Kate and Ashley to disrobe in Playboy since they turned 18 - and he's now launched a renewed bid to tempt them out of their clothes for a special celebratory photo shoot. A source tells American magazine Star, "Hef thinks the twins are every young man's fantasy." But insiders insist the Olsens are holding out for a more classy magazine deal, telling Star, "They're all about high-end fashion these days. They want to do Vogue."