I have always worked on the assumption that Kirk must have commanded another ship before Enterprise (I love the 09 movie but always found the idea of a cadet being promoted to captain of the flagship of the fleet somewhat hard to swallow).
But given how much we know about the previous command histories of other captains, I think it's an interesting little oddity of the original series (and movies) that we never got a definitive and unambiguous answer one way or the other onscreen.