http://www.chud.com/index.php?type=news&id=12002

A lot more about the characters that will be in the Dragonball movie.  I watched most of Dragonball and almost all of Dragonball Z, but I don't really recall Goku being 18. I'd suspect it would have happened near the end of Dragonball.   It looks like the movie is almost definitely taking those well known movie "privileges" to screw with the actual story in any way they want.  I won't list them, but it is pretty obvious, unless this story is so small that I never saw it.  The closest I know of is the King Piccolo Saga, but that occurred with Goku at a much younger age.  

Regardless, I can't see this being a very good movie, but who knows?  Maybe it'll be a treat for fans?  (I won't hold my breath...)