You're right about the need for new challenges as we age. Workouts for the brain are as important as physical activity is for the body. In my new book, Healthy Aging, I describe various ways to keep the mind agile and boost memory and concentration. I've long recommended card games and word puzzles as worthwhile traditional pastimes to exercise the brain.
But if you're looking for truly new challenges for your brain, the best mental workouts I can think of are learning a new computer operating system and learning a new language. If you've used a computer, you're familiar with the frustration of learning a new operating system - it wears you out. But this kind of challenge is exactly what is needed to force change on the brain's neural network so that it will stay flexible and young.
If you haven't used a computer very much, now's the time to learn. It may drive you crazy for a while, give you headaches and make you wish you never decided to take up the challenge. But it will open a new world for you once you learn all its complexities and give your brain a good workout in the process.
Learning a language is another perfect challenge to take on now that you've retired. Some people have a natural ear for language and learn quickly, but anyone who can hear and imitate sounds can learn a new language at any age. And you don't have to master it; it's the attempt to learn that gives the benefit. This type of learning draws on "fluid intelligence," the ability to stay focused and manage attention while ignoring irrelevant information. Fluid intelligence is one of the first aspects of brain function to suffer as age takes its toll on the mind. Learning another language should be more protective than any supplements or smart drugs designed to stave off cognitive decline.
I speak Spanish and used to speak German. I'm determined to brush that up and one day learn Japanese.
Andrew Weil, M.D.