Bill, Can you confirm the units of measure?  You wrote nanograms per liter, but I am wondering if you really mean nanograms per deciliter, as that would make more sense with the numbers that you have given. 

If the numbers are, in fact, in nanograms per deciliter, then I would follow the advice of the first doctor.  Levels of 6320 ng/dl for a child born at 6 mos gestational age very likely reflects the fact that your son was born extremely premature, not that he has CAH. 

I think the first doctor’s suggestion to slowly wean him off meds, while closely monitoring him, is a very reasonable and good suggestion, under the circumstances.   However, I would also ask him if your son’s levels might continue to be slightly higher than normal for a little while, until his adrenal glands continue to mature.  (You didn’t mention when your son was born, and if he woudl still be in the womb now, if he hadn’t been born so early.)  

Personally, I don’t think the second doctor’s suggestion to wait till your son is 2 years old to try to wean him off meds, makes much  sense.  There is nothing "magical" about the age of "2", in this situation.   Giving your son meds that he may not need for a full two years would do much more harm than good...the hydrocortisone could compromise his growth potential and the Florinef could give him problems with high blood pressure. 

I would also, personally, forego the genetic testing at this time.  In some situations, genetic testing can certainly be a valuable adjunct to other laboratory testing, but in other situations, I think it adds very little new information and, sometimes, can even make the situation MORE confusing. 

At any rate, please do confirm first the units of measure, as that makes all the difference in how to evaluate the situation.