A surface to air missle can target up to 15,000 feet. The flight was slightly above 13,000 when it was hit.
Of course, the next problem with the missile theory is that a painstaking reconstruction of the wreckage clearly shows that the plane's metal was twisted outward from the main fuel tank area deep inside the plane and no evidence of an inward explosion on the outer skin was ever found. Next, no evidence of missile pieces or traces of missile explosive chemicals was ever detected, even in minute quantities. I'm afraid the missile theory for flight 800 is destined to become the "grassy knoll" of aircraft crashes for those bent on seeing conspiracies everywhere.