To get a good idea of your fitness level before starting an exercise program, try running or walking for 12 minutes and see what kind of distance you can cover. If you cover a mile or more you're in decent shape. You should feel good about where you are. Start your exercise program at a more vigorous level if you do well. Don't feel bad if you don't get close to a mile. Most beginners can't. You just have to start out at a pace that is comfortable for you and increase it as your fitness improves.