You cannot go back to the Archives and correct an old document. What you can do is contact the American Civil War Research Database, Historical Data Systems, Inc. at
http://www.civilwardata.com
and have them make note of the age discrepancy.

As to his burial, what I provided was found at Ancestry.com and only informs as to the order for his headstone and to whom it was delivered. Where it was placed was not stated.