Exercise is the only real fountain of youth that exists, " says Jay Olshansky, a professor of medicine and aging researcher at the University of Illinois at Chicago. " It's like the oil and lube job for your car. You don't have to do it, but your car will definitely run better. " Study after study has documented the benefits of exercise to improve your mood, mental acuity, balance, muscle mass, and bones. " And the benefits kick in immediately after your first workout, " Olshansky adds. Don't worry if you're not a gym rat. Those who see the biggest payoffs are the ones who go from doing nothing to simply walking around the neighborhood or local mall for about 30 minutes a day. Building muscle with resistance training is also ideal, but yoga classes can give you similar strength-training effects if you're not into weight lifting.