Are you worried about his becoming too tall?   I don’t think this is something that people with CAH generally have to worry about.  Is he in puberty?  I think he’s having his pubertal growth spurt which I think lasts a few years and is accompanied by very rapid growth - 3 - 4 inches a year.   Have the doctor do a bone age.  I don’t think they would give him Lupron (?) at this point to slow puberty because 12 isn’t really very young for a boy to start, and he’s already tall enough that he probably won’t be very short.