I suspect he was enlisted/conscripted into the army sometime after February, 1864 when the conscription age was raised from 45 to 50. There are no surviving company muster rolls post December, 1862.
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Thomas Knight, Private, Company H, 17th Regiment Alabama Infantry, captured at Franklin, Tennessee December 17, 1864, admitted to USA General Hospital, Nashville, Tenn., December 26, gunshot wound right leg and arm by Con. ball, age 46, sent to Camp Chase, Ohio prison camp, forwarded to Point Lookout, Maryland prison camp for exchange May 26, 1865, released June 14 on subscribing to the Oath of Allegiance to the United States, description: resident of Mobile, Alabama, dark complexion, dark brown hair, dark blue eyes, 5' 8-1/4"
M311: Compiled Service Records of Confederate Soldiers Who Served in Organizations from the State of Alabama
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THE SEVENTEENTH ALABAMA INFANTRY.
The Seventeenth Alabama infantry was organized at Montgomery,
August, 1861.
Serving first at Pensacola, it was present at the bombardment of
that place October 9, 1861. The Seventeenth was distinguished in
the battle of Shiloh, taking a prominent part in the capture of
Prentiss' division; served at Mobile from the autumn of 1862 to
March, 1864; then joined the army of Tennessee, and, under the
command of Gen. E. A. O'Neal, afterward governor of Alabama,
fought during Sherman's campaign from Dalton to Lovejoy's
Station.
It was engaged in the battles of Resaca, May 8th, May 13th to
15th; Cassville, May 19th to 22nd; Kenesaw Mountain, July 8th to
30th. At Peach Tree Creek its commander, Major Burnett, was
severely wounded, and Captain Ragland was killed at Atlanta.
The regiment was engaged in the battle of Atlanta, July 22nd; at
Jonesboro, August 31st to September 1st; and Lovejoy's Station,
September 2nd to 6th. The Seventeenth regiment lost heavily at
Franklin, November 30th, and at Nashville, December 13th to 16th.
Its field officers were Col. Thomas H. Watts, who became
attorney-general of the Confederate States; Col. Virgil S.
Murphy; Col. J. T. Jones, temporarily assigned; Lieut.Cols.
Edward P. Holcombe, Robert C Farris, and John Ryan, temporarily
assigned, and Maj. Thomas J. Burnett.
Source: Confederate Military History, vol. VIII, p. 111