I'm rather sure this is the same fellow. Unfortunately there are two different ages given. Birth and death dates would only be available through Federal Census data, or information in your family papers. Civil War Confederate records rarely contain birth dates, death dates are found once in awhile, but they usually originate from modern contributors to databases.

I was unable to find him in the 1860 Federal Census, Ancestry.com

There were two other William J. Beard's in Mississippi Confederate Units, these were:

William J. Beard, 4th Sergeant, enlisted in Captain A. Archer's Company, Lowrey's Regiment, Mississippi Volunteers, * March 17, 1862 at Itawamba/Marietta, Miss., reduced to ranks for inefficiency May 1, 1862, last shown present on the Mar & Apr, 1864 muster roll, recorded on a register of Prisoners of War at Memphis, Tenn. - Deserters from the rebel army, ______ 4, 1864, resident of Marietta, Miss., light complexion, light hair, grey eyes, 5' 10", age 32, swore Deserters Oath of Allegiance to the US at Memphis, Oct. 1-15, 1864

* This company subsequently became Company F (Southern Farmers) , 32nd Mississippi Infantry

.................

William J. Beard, 4th Corporal, Captain H. G. D. Brown's Company, Artillery, (Seven Stars Artillery) Army of Mississippi**, enlisted September 1, 1861 at Hazlehurtst by Capt. H. G. D. Brown for one year/September 30, 1861 at Bay St. Louis,] by Lt. Hunt, promoted Sergeant, n.d., captured at Port Hudson, Louisiana July 9, 1863, released on parole July 12/13, 1863, no further records

** This company subsequently became Capt. Roberts' Company, Mississippi Artillery

M269: Compiled Service Records of Confederate Soldiers Who Served in Organizations from the State of Mississippi