Our expert says:
you should not be concerned. with the onset of puberty, the penis starts increasing in size. due to the fact that your 13 year old son is at the age of puberty onset, this may account for his larger penis size. at the age of 13, your younger son will most assuredly also increase in size. until that time, it is very important not to draw your younger son's attention to the fact of his smaller penis size - this may lead to severe psychological issues in latter life.
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