Brain Myth #4: Memory decline is inevitable as we age.
Many people reach very old age and are still sharp as ever. Genetics clearly plays a role in "successful aging," but how we live our lives on a day-to-day basis is also critical. To help your brain age well, you can:

Perform physical exercise (especially aerobic exercise)
Engage in intellectually stimulating mental activity
Eat a healthy diet
Maintain social connections (spending time with friends and family members, for example)
Learn to manage stress
Develop a positive attitude toward yourself and your world

http://www.aarp.org/health/brain/aging/myths_about_aging_and_the_brain.html