@cbssundaymorning: After a career as an educator and social worker, Diane Shiffer found a whole new audience online. Now known as @shifferdiane, she’s embraced the “Nana vibe” and charmed nearly two million followers. Faith Salie catches up with Shiffer and fellow grandfluencer Barbara Costello (aka @brunchwithbabs) to explore how these stylish seniors are turning social media into their second act. #retire #social