Is it abnormal for a 13-year-old male to be stronger than 20 percent of the world's male adults?

Abnormal is not a word with much value when discussing body types or capabilities. You are what you are, and if it is normal for you, then that's pretty much the end of the discussion. On the other hand, if the strength has come from steroids or excessive workouts, that would certainly be considered abnormal. The human body needs to mature and finish it's growth cycle before attempting to establish that kind of muscle mass through exercise. Notice that most men start to put on muscle during puberty. It's part of the natural process. Toward the end of puberty, at around 18 to 20, the muscle mass becomes far more defined and a man can continue to put on muscle as part of the maturation process. Unfortunately, a lot of us also put on a big gut during that period. Simply put, if you have been part of some kind of exercise/steroid cult that resulted in your strength, it's not normal. If it's just part of what you inherited from your parents, don't worry about it.