Want the secret to a happy, long life? It's exercise. Sure, there are plenty of other anti-aging tips to prevent disease and add years to your life, but if you don't keep fit, you won't be able to enjoy those later years. Maintaining your fitness not only helps you look and feel young, but also allows you to engage in fun activities that you might not have had the time or money to do earlier in life.

It's best to make exercise a life-long habit, but no matter your age, you can start being physically active to increase your mobility and strength to make everyday tasks easier and more enjoyable. We spoke to Colin Milner, the founder and CEO of the International Council on Active Aging, about the best ways to ensure that you feel young as you age.

Find a fun way to raise your heart rate
Many people will claim to know the best kind of cardio, but all that really matters, says Milner, is that you find something you love and that you'll want to do for at least 150 minutes a week. "What ends up happening is people start with something that they don't really enjoy, and then they drop out. So the first step really is to say: What do I want to do?" Your preferences and personality are more important than choosing a form of exercise that demands the highest calorie burn or heart rate. That's because, for most of us, keeping up with exercise is the biggest health hurdle. Choose something you'll want to continue. Do you prefer walking outside or are you easily swayed by bad weather? Do you like the convenience of a gym or do you find gyms stifling? Maybe you enjoy group classes or having a workout buddy to keep you motivated. And consider broadening your horizons beyond traditional workouts: For some, gardening or walking a dog might be the best ways to incorporate extra activity.

Keep your muscles strong
"By the age of 80, 46 percent of the population cannot lift 10 pounds," says Milner. That number is startling, because it doesn't just mean that people can't lift a dumbbell; it means they might not be able to lift a suitcase to go on a trip or carry their groceries home from the market. "That has a huge impact on somebody's quality of life." Milner explains that while we look at strength training as a matter of benefiting our health or improving our physique earlier in life, it's a matter of maintaining our independence later in life. "My grandmother is 103 years of age and she wakes up every morning and pulls out her dumbbells from under her bed," shares Milner. He encourages everyone to make time for strength training at least twice a week, and to be sure to train every major muscle group. It's best to start early because, Milner explains, between the ages of 30 and 70, we lose roughly 50 percent of our strength if we are inactive, and it's much easier to maintain muscles that you've gained earlier in life than it is to suddenly try to build them when your muscle mass is already on the decline. Luckily, major gym equipment is not necessary for strength training, and you can even do it while watching TV.

Build some balance
Balance isn't something you hear many personal trainers talk about when you're young, but if you want to stay young, balance is key. Milner says one in three people over the age of 65 fall every year, and the main reason is that they don't have proper balance. Unfortunately, at that age, falls also come with huge consequences. Yoga and tai chi are just two ways to help develop balance. There are also balance boards and you can simply do some of your other strength training exercises with an added balance element (such as biceps curls while standing on one leg). To prevent falls, it's important to be stable on your feet and to respond quickly, says Milner. Though these skills might have come naturally years ago, it's important to train for them later in life.

Get flexible
Doing morning stretches or beginning a yoga practice can do wonders for keeping you feeling young and flexible. Like strength, flexibility is something that we naturally lose as we get older, and it's much easier to maintain it than it is to try to build after you've lost it. Milner says the practical benefits of stretching are endless for people in their later years. "Think about keeping your driver's license: One of the things you have to be able to do is turn your head. If you don't have the flexibility to do that, you have a problem," he says. Being flexible can help you avoid injuries and falls, which will go a long way in keeping you young.

Want more strategies to turn back the clock? Get eight healthy anti-aging tips.