According to Gretchen Reynolds, author of The First 20 Minutes: Surprising Science Reveals How We Can: Exercise Better, Train Smarter, Live Longer, current scientific evidence suggests that exercise not only helps you live longer but it also keeps you vibrant for the length of it. All the way down to your DNA! Exercise and simply staying active can lengthen your telomeres and keep your mitochondria healthy. In fact, it is suggested that a majority of the physical signs we once thought were caused by aging are actually the result of being inactive.