Given the circumstances that I'm currently in, and the state that my mom has come to be in, I can't help but sit here and think that the most important exercise we can get in our lives is mental. You can work your body as much as you want, and even extend your life through these physical pursuits. Unless you constantly exercise your mind, however, who can say how many of these extended years will be happy, harmonious years? How many of them will be spent in misery, wishing that you were no more for this world? How many years will you spend in regression, not really knowing the current or what is going on around you?
I'm not trying to downplay the importance of physical exercise here, not at all. Our country is obese, that is a fact. More people need to get off their lazy asses and work out. But just as many people, and probably even more, need to work their minds a lot more than they currently do. It's nothing terribly difficult. In fact, mental exercise is even easier than physical. You can remain seated on your lazy ass while you do it!
There are any number of things you can do to exercise your brain. Pick up a book, a magazine, or a newspaper and start reading. Do what I'm doing right now and write down your thoughts. Grab a deck of cards and play a game of solitaire. Work on a crossword puzzle or a sudoku puzzle. Troubleshoot a problem in something; a car, a computer, even in your fridge. Any of these activities and thousands more will work your brain and keep it fresh. All you need to do is think, keep thinking... be creative, solve problems, learn new things. This is how you exercise your brain. This is how you keep your brain young. And most importantly, this is how you ensure that your brain will stay fresh through your life, and your final years will be happy ones, not years spent wishing it would all end.