QuestionLets say there are two kids, both age 16.
One of them is about 5'10" 160 pounds, very physically mature, muscular and extremely strong for his age. Has a lot of facial hair growing, chest hair, etc.
The other one, is about 5'10" also, but he is about 140 pounds, very skinny, has not yet started to grow facial hair or chest hair and is nowhere near as strong as the other one.
Lets say neither of them ever lift weights or do anything that involves strength training. Will the more physically mature 17 year old always hold a strength advantage over him because he was able to develop muscles earlier?
In the design of the human male, God made our muscles such that when they are taxed, additional muscles grow to make the task easier. The exact mechanism that triggers that growth is not known, though that hasn't stopped a lot of people from guessing, and even more people making claims so they can dip their hands into your bank account. Interestingly, the opposite is also true. If a muscle isn't stressed, it will eventually wither away (the process is called atrophy). This is why someone who has been ill or injured for a long time has to work to regain their strength once they recover. Actually, your body is constantly recycling your muscle fibers. Stressing the muscles just causes them to grow faster than they are taken apart.
Two young men, even though they are not in training, will still be using their muscles daily, such as by walking between classes. The difference between this incidental exercise will make a difference in strength.
Though one starts behind the other in development, eventually they will reach the same stage because there are only five stages. But two individuals won't necessarily develop the same strength. The less developed young man could become larger, the same, or stay smaller. Some of it depends on a man's genetics. Some men are disposed to building larger muscles. But all men can increase their muscles through exercise.