Roster of Confederate Soldiers, 1861-1865 does not show a WILLIAM YOUNG GARDNER but does show:

Gardner, William KY 10th (Johnson's) Cav. Co.D 2nd Lt.
Gardner, William KY 1st (Butler's) Cav. Co.F
Gardner, William KY Cav. 2nd Bn. (Dortch's) Co.C 2nd Lt.

Roster of Union Soldiers, 1861-1865 does not show a William Young Gardner but does show:

Gardner, William KY 24th Inf. Co.F
Gardner, William KY 48th Inf. Co.H

and

Gardner, William D. KY 17th Cav.
Gardner, William L. KY 34th Inf. Co.B
Gardner, William R. KY 3rd Cav. Co.L 1st Sgt.