According to most sources, Janet Yellen is still the front-runner to succeed Ben Bernanke as Chair of the U.S. Federal Reserve. If she receives the appointment, @liuk__ points out that she would be the oldest Fed Chair (at appointment time) in history.
The oldest appointment to date has been Arthur Burns who began his term at age 66. Yellen is currently 67. The youngest ever to hold the seat was Marriner Stoddard Eccles, who was appointed at age 44.