After age 30, muscle mass declines at a rate of 3 to 5 percent each decade, according to Harvard Health Publishing. Do the math and you can see where you stand at age 50 if you've been living a sedentary lifestyle. But don't panic. It's never too late to start a muscle-building exercise routine. If you choose the right program and stick to it, you'll reap the benefits of increased lean muscle mass in no time. Building lean muscle mass at any age can give you a new lease on life. Most important, you'll grow stronger and feel better able to handle the tasks of daily living. You won't get fatigued as easily performing chores