Here are a few options for you to ponder:
(1) Healthy Diet - research the best foods to eat and the best supplements to take. You could even go a step further and research the best ways to live to 100. (Eating less meat appears to be a key factor.)
(2) Genealogy - Research your family tree. The Family Search website and Ancestry.com are your best choices here. Family Search is free, but Ancestry.com charges.
(3) History is always an interesting subject and the History Channel on television offers many neat programs, especially if you would rather watch re-enactments rather then read.