If you are under 13, you’d be too young to start intense weight lifting. Don?t let this put you off exercise though, as low impact exercises such as push ups and chin ups can be a great way to start. At 15 or 16 depending on your natural development, most teens can start using exercises such as squats and deadlifts. Ensure that you get advice on how to do these correctly, as incorrect technique of these may lead to injury. Besides developing good form early means this generally will stay with you in later years, plus there is an old saying which goes “good technique equals good gains” so keep this in mind.
Include protein and complex carbohydrates as they are the best source of energy and muscle building nutrients to help you gain muscle whilst at the same time keep you healthy. Rest is crucial to developing muscle. Without adequate sleep, (8 hours a night) you will not repair and grow muscle to as well as what’s possible. You will also lack energy for your next training session. So be sure to rest after training and as a general rule do not train a body part whilst it is still sore from an earlier training session. As a beginner, ensure you persist with your scheduled workouts, and do not put them aside for other plans. Results come with dedicated consistency.
Starting training at a young age is a great way to get fit and stay healthy. So bring with you a determined, patient attitude & get advice so that you use the right exercise technique.