Bikes are a great way to get healthy. If you've been inactive for a long period of time, take it easy at the beginning to be safe. Keep your rides short (less than an hour) and often (4-5 times a week) to let your body adjust to your riding position. To avoid injuries, never ride as hard as you can while just starting up. After a week or two of riding, check in a local bike shop, and ask if there is a local group ride you could join.