The fact that your ancestor fought in the Civil War and lived in a southern state does not mean that he was a Confederate soldier. “Southern Loyalists” were citizens of southern states who sympathized with the northern cause to preserve the union. Approximately 150,000 of them (or more) became Union soldiers.
Contrary to popular belief, many Confederate veterans did receive pensions. They were provided not by the U.S. Federal government but by the individual southern states. Although Confederate pension files typically contain fewer documents than Union ones, they are nonetheless very useful for family researchers.
The American Civil War was fought from 1861 to 1865 and the average soldier was 18-45 years old. So if you have a white, male ancestor who was born between roughly 1816 and 1847 and lived in the United States in the early 1860s, then he probably played some part in the Civil War.