Eric Rackow, M.D., says staying physically and mentally fit will help you live to be 100. Puzzles are an easy way to activate the brain, and if you start doing one weekly when you're young, you'll be in a much better position when you're older. Crossword puzzles, trivia shows like Jeopardy and math games like Sudoku are all good brainteasers, experts say. Studies also show that playing a musical instrument will help preserve mental processing. More From Forbes: America’s Healthiest Cities World’s Most Dangerous Places to Breathe The ‘Healthy’ Choices That Are Costing You The opinions expressed are solely those of the author and do not necessarily reflect the views of Comcast.