Test your recall. Make a list — grocery items, things to do, or anything else that comes to mind — and memorize it. An hour or so later, see how many items you can recall. Make the list as challenging as possible for the greatest mental stimulation.
Let the music play. Learn to play a musical instrument or join a choir. Studies show that learning something new and complex over a longer period of time is ideal for the aging mind.
Do math in your head. Figure out problems without the aid of a pencil, paper, or computer. You can make this more difficult — and athletic — by walking at the same time.