I think the large (or perhaps "absolutely vast" is a better way to put it) number of teenage fans Star Wars had back in the late seventies (and we are not only talking about the "geeky" kids here) is a pretty big testament to Star Wars having not been a kids movie.

Name one single kids movie that was released in the last ten years that has wound up with a large number of teenage fans. This sort of thing just doesn't happen.

Perhaps Star Wars is hard to place because it was something so new, there really wasn't anything else like it back in its day. Sure, there were plenty of sci-fi films, but Star Wars had a certian unique quality to it. Star Wars really caught audiences off guard and they fell in love with it, young and old alike. Nowadays Star Wars' style is often emulated by kids movies, perhaps this makes it easier to retcon it as strictly a kids film, that adults just happened to like (which is what Lucas claims it was all along). But evidence still indicates that it was intended for an audience much larger than just children.