Forbes: Spanx inventor Sara Blakely is youngest self-made female billionaire Spanx founder Sara Blakely at the Spanx Fall 2012 Fashion Week Presentation in New York in February. Skip Bolen, Getty Images for Spanx / February 13, 2012 March 9, 2012 Spanx inventor Sara Blakely is a billionaire at 41 years old, according to the annual Forbes magazine list of billionaires. Blakely, the creator and owner of the line of women's and men's slimming, smoothing undergarments, is the youngest woman ever to make the list as a self-made billionaire, meaning she didn't inherit or marry into the money. According to Forbes, Blakely was 29 when she was looking for something flattering to wear under her white slacks. She invested $5,000 - her entire life savings - to start the company.