You might want to recheck your records, the Conscription act of April 16, 1862 included all males between the ages of 18 and 35.

These fellows you mentioned may very well have originally signed up for 12 months and were subsequently discharged on the date you note as being over the age of conscription and having served their originial obligation.

I see many of these discharges in men of the 43rd Tennesse above and below the stipulated ages for conscription, as an example " . . . discharged November 16, 1862 at Lenoirs, Tenn. by reason of his term of enlistment having expired and he being over age."

George Martin