Well, my daughter is keeping my mind active by making me help her study for tests and quizzes.  I know all about eukaryotes for example and I've also been refreshing maths and chemistry lately.  I feel as though I've forgotten just about everything I had ever learned in school but it does come back to you once you look at it again.  Helping her with computer programming was the most fun for me but that's her least favourite area of study