Most teenagers believe that right after they hit puberty, it would be 'super cool' if they joined a gym and started bodybuilding. That's actually more harmful than it sounds because, during puberty, your body is still developing and maturing. The truth is that a person's bones don't stop growing till they're about 20 years old, which means that at 15, you're still developing bone mass. If a lot of loads is put upon a skeleton that has not yet reached its maturity age, it will not only stunt your growth but might also result in permanent injuries. Strength trainers tend to ignore this fact because more people mean more money for them. However, any doctor worth his salt will advise school goers to NOT do bodybuilding. Co-ordination is another problem with teenagers. Dead-lifts and squats (with weights) require the proper body posture and form, a lack of which will result in immediate injury. Since the bodies of teenagers are still growing, their brains find it a little difficult to take account of changing sizes and proportions. Needless to say, one requires a certain amount of maturity as well as good judgment to be lifting weights for bodybuilding. Up until the age of 18, the judgment skills of an average child are yet to develop, and this is the reason why most countries accept children over the age of 18 to be treated as adults. Younger children also tend to show off a lot, like lifting a lot more weight than their bodies can handle. Most teenagers who lifted a lot more weight than they should have, complained of regular muscle strains, especially in the lower back. The most appropriate age to start building your body would be at the age of 20. By that time, your body is fully developed, with your coordination and judgment being under a lot more control of yourself. This is the one time of your life which will allow you to lift maximum weights in the shortest recovery time possible. The age between 20 and 30 is the perfect age to bulk up, and you should take advantage of that fact. This, in turn, will ensure that your body will be a little less affected by the loss of muscle that occurs in old age. At the age of 20, the average recovery period is a maximum of two days after a strenuous heavy weight workout. And by the time one reaches the age of 30, that recovery period becomes twice as much - four days. Of course, the recovery period does vary from person to person, depending on the diets they take, supplements, their genetic structure etc. Keep in mind though, when you've become a veteran in bodybuilding, sometimes your body might require up to 7 days of recovery period when you lift extremely heavy weights, irrespective of your age. Parents should also try and not encourage their teenage sons to life weights. They might end up gaining muscle but at the cost of losing the strength of their bones. At that age, the most recommended exercises include cardio, aerobics, and light weight lifting so that one can start easy with one's coordination and judgment.