Physical decline as the body ages is inevitable, something to be grumbled about, accepted and dealt with. That fundamental law has not changed, but the way we manage aging has. Getting older need not mean getting weaker, at least not until the end is truly near. Just look at athletes like Roger Federer and Jo Pavey, who are still going strong as they reach mid-life. Here’s how you need exercise to stay in tip-top shape as you age.