He was my great, great grandfather born in 1817. I just ran across your 2011 query and understand the confusion.
He apparently enlisted as a captain in Sukalawsy's(sp) Regiment in 1861, but resigned in 1862. He is shown elsewhere as a Captain in the Armstrong Guards, a Home Guard Company, which seems more appropriate in view of his age. I am not sure whether he continued in that capacity after 1862.
He was the brother of Frederick Hillsman Farrar
His nephew, Thomas Prince Farrar II was the one who died from wounds received at Port Republic.
He also had a son, Thomas Prince Farrar, Jr, who was too young for the Civil War.