Confederate service record documents do not usually indicate age, hence, in his case, this is not unusual. It would appear only on special forms not universal throughout the army.
Documents for his units are but few, however, it does not appear that he was at any time a prisoner of war. When paroled, his unit was surrendered in mass and never saw a prison. If a prisoner, we would usually see Federal papers documenting the fact.
Confederate military authorities were usually strict on discharging men under the age of Conscription, which was originally age 18 until December, 1863 when it was reduced to age 17.
Nonetheless, as in WWII, many youngsters were able to fake it and serve in the military, but not knowingly.