I believe that the then Group Captain Dereck Kingwell, was the youngest pilot to make Group Captain. At the age of 19 he became CO of the RAAF 82 wing, flying the B24 Liberator.
Stayed in the RAAF after the war and ended up as a Air Commodore.
Great pilot and CO, only died in recent years.
I suspect that age had nothing to do with his rise, just the right man for the job.
Regards
Col