I'm never gonna retire," Joan Rivers declares, sitting down to reminisce over old photos at her Upper East Side penthouse June 5, three days before her 80th birthday. "Yesterday somebody said, 'I'm 62 and I'm so tired.' I thought, 'Are you crazy? Let's go play tennis!'" She may now be an octogenarian, but for the star who got her start doing stand-up in the '50s and continues to dish out her biting brand of celebrity criticism on E!'s Fashion Police
, the notion of slowing down seems absurd. "I feel great," quips Rivers, who's taken over E! for a week to mark her milestone birthday. "I don't know if it's vitamins or what, but it's working."