Nobody ages backward. Now that we have that unpleasant fact out of the way, let's get to some good news: You don't need to be a genetically blessed model or have a plastic surgeon on speed dial to keep your body in remarkable shape. Instead, just dive into the closest thing we have to a fountain of youth: fitness. With the right workout strategy, one targeted for your age and physiology, you can fight back against the inevitable slowdown, build muscle and keep your weight in a happy place. Whether you're blowing out the candles on your 30th-birthday cake or planning a big 5-0 bash, follow our decade-by-decade game planbased on advice from scientists, nutritionists and fitness prosto get the body you want right now.