No, you can start exercising any minute, any day. Before you start you must know your body is sensitive and definitely not for experiments. Instead of following diet plans and exercise plans on internet buy a gym membership where a real trainer can guide you. This is very important yet neglected by people. Exercise is a serious job as it is all about building your body’s strength, endurance and flexibility. It depends on your current body shape and size, age, gender and overall lifestyle. Every person has a different set of goals in gym. Start building muscles!