pulled up some pics of civil war era pocket knives and I would say it is possible yours is that old but I really don't know. maybe someone else here can be of more help
Your knife is a serpentine stockman's knife, a pattern that was not available during the CW. It is most likely a 20th century knife by pattern, and like most rusty old knives the exact age will never be known since age determination of old knives is done by the markings on the blades.