The more you do to stay active as you age, the lower your chances are for things like heart attack and stroke. Your doctor can tell you what type of exercises are best, and for how long you should do them. You’ll probably shoot for 150 minutes of moderate aerobic activity a week, like a brisk walk or an easy bike ride. Mowing the lawn or a heavy cleaning session counts, too. And you don’t have to do them in 30-minute chunks.