For years my son was the shortest child in his class at school and we he got the the age of 13 years  was 145cms (approx 4ft 8") and had the bone age of a 6 year old (which is unusual for a child with CAH).  His endocrinologist  recommended testosterone injections to advance puberty (because of the bone-age delay) but I wasn’t happy and requested a second opinion.  Seemed odd to me to give male hormones to someone with CAH, when we have been suppressing them with treatment for years!  His new endocrinologist didn’t believe the bone age on sight, as my son had his 12 year molars (has this boy?), however another x-ray proved the first result accurate and 7 years delayed.  Blood tests however (LH & FSH) proved he was just starting puberty, with testicular volumes of 4mls.  My son’s hydrocortisone dose was decreased to 7.5mgs a day (from 12.5mgs, which showed over-suppression) and he went through puberty naturally (dose was increased again along the way).  His bone-age advanced quickly, which I am told was bound to occur because of the testosterone produced during puberty.  My son will be 17 years old in March, is 5ft 8" and still growing (bones have not fused yet!).  

My advice would be, leave this lad for a few more months to see if puberty occurs naturally - perhaps get a second opinion too?  Testosterone injections are an option and will advance the bone-age and puberty but will not increase final height and should be used as a last resort.