This New York Times article has some great information on keeping the brain young, or actually read as: remembering things you learned previously. Reading viewpoints and information different from your own is the key as it challenges the brain.
Read for yourself.
We become too complacent by reading information from people who think just like us. I have a variety in my blog roll but should probably add a few more counter voices. I am sure all of us could do more as the article says.
Since the vast majority of the public do not, another good reason to instill this in youth in order to create a generation of learners that never stop learning.