At the age of 19 the "average" size is 6.2 inches erect. I don't know his exact size nor do I know what type of doctor you took him to.
If you didn't, you should take him to a urologist for evaluation. There really is not a whole lot that can be done on size. The pills/creams etc do not work. There are some surgeries that are being performed, but are not 100% and do cause complications. If you did take him to a urologist I would suggest another doctor just for a 2nd opinion as well. You may want to even inquire as far as an implant as well. But do get another opinion.
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