Here is the grave of the man who enlisted from St. Clair County in Co. A, 10th Alabama. His birth date of Nov. 1839, would indicate that he was, indeed, 21 years old in June 1861, when he enlisted.

http://findagrave.com/cgi-bin/fg.cgi?page=gr&GRid=27766544

Here is the grave of the man Pam is inquiring about. It would seem that the placement of a Confederate stone indicating service in the 10th Alabama on his grave is in error.

http://findagrave.com/cgi-bin/fg.cgi?page=gr&GRid=39438060