I have 17 OH deficiency. I’m 38 and been on cortef for about 28 yrs. We went skiing at Big White in Canada last year and camping at Beartooth mts in Montana and could definitely feel the effect. Don’t know if it was my CAH or not but I seemed to be moving slower than all the others we were with, and at Big White I had a migraine for 1/2 a day. i am a person with a high energy level also and in fairly good shape.I know in general people do get dehydrated at higher elevations, and I drank lots of water and gatorade. So that is my suggestion. Does he get sick in airplanes?

Hope this helps some.