Bryan,
The use of the younger troops for courier service was one of Gens. E. Kirby Smith & J.B. Magurder's "pet" projects, they had Fulcrod's Cadet Battln. formed for that duty in Texas in mid 1863, to releived older ones for combat duty. But the battln. was consolidated, with Border's Battln. to form Anderson's regiment, guarding federal prisoners at Camp Ford, Texas after the Red River campaign.
Mike Thompson