Quadqueen, its true if the meet director is following the USAG Rules and Policies. The meet director is also required to publish the age guidelines for that meet. If the particular meet is not a qualifier for your particular state meet, then maybe they have some wiggle room, but I don't think its a good idea. As long as the competitors know what the criteria is it should be fine.
As for what ages and age ranges are in a particular group and what that group is called, it is completely up to the meet director as he sets up the scoring software. The label that goes on a group is chosen, hopefully, to distinguish one group from another. Knowing what age group an athlete is in before the meet should be known to the coach since it is usually printed on the score cards/sheets that the coaches get.