Pssst . . . want to get in on the ground floor of a knock-your-socks-off investment opportunity? Not up for another Ponzi scheme? No worries! The investment: 30 minutes of exercise a day. The return? An extra 2.8 high-quality years.

Fit people in their 50s are twice as likely as their unfit classmates to celebrate their 85th birthday. Even better, fit doesn't require climbing Mount Everest or doing Ironman triathlons. All you need is half an hour of physical activity a day, plus some strength training. If you've been sitting on the sidelines, adopt this three-part plan as your stay-young investment account:

• Step 1: Walk for 30 minutes every day. Make a daily, brisk half-hour walk your first fitness goal. Get a buddy and you'll get younger two ways -- companionship and exercise. Or walk three times a day for 10 minutes. Aim for consistency. Think you don't have time to exercise? Discover how interval training helps you burn more calories -- and belly fat -- in a short workout.
• Step 2: Sweat. After 30 days of daily walking, step things up. Add something sweaty 1 hour a week: Take an exercise class, bike, hike up hills. Go to the health club you joined. A great predictor of how long and well you're going to live is how well you can exercise your heart and how fast it recovers from a maximum interval. Here's how to measure your heart rate recovery.
• Step 3: Build strength. Find an extra 30 minutes a week -- in one session or not -- to build muscle by lifting weights. Learn how proper form helps you get more out of your strength training workouts.

No time? Do walking meetings. And turn up the intensity when sweeping, mopping, mowing the lawn, walking the dog, or gardening to make you younger and give you more energy. Here are more ways to turn your daily tasks into exercise.