The description of your son suggests he is under-suppressed.  Of greater concern than any size issues "down there" is the potential early onset of puberty, and whether his body is aging faster than it should.

This is something I had to deal with as a child, whose bone age was 7 when he was 4.  It wasn’t normalized until I reached 12 -- by being on a strong daily dose of prednisone during those 8 years.  Fortunately for me, it was caught in time, and I did not go through early puberty.

Get to your endo and have your son’s levels tested, as well as his bone age.  Getting these results is the only way to really know what is going on.

Good luck, and may the new week embrace you warmly -- Eric 

PS -- Having survived all the issues of growing up as a male with CAH (which pale in comparison to what the females go through, but are still significant challenges), I’m now a happy, healthy 40+ male with three lovely children.  I maintain a daily regimen of hydrocortisone.