In Episode III, Palpatine tells Anakin a story about Darth Plagueis, a Sith Lord who learned how to prolong life through the dark side of the Force in order to get Anakin interested in the dark side, since Anakin tells Palpatine he has been having dreams of Padme dying. Palpatine reveals that Darth Plagueis was real and did know how to prolong life... until Palpatine killed him. Palpatine's real age is subject to all kinds of retarded EU fuzzy arguments. I say he's in his 100s by the time of ROTJ.