I agree that would stink to have an "all age" session. In our area we really don't have L3's so I am not familiar with how their meets run, but in L4 this past year it depended on the meet as to how the sessions were broken down into age groups. Larger meets sometimes broke ages down (ex 6,7,8) and smaller meets (invitationals) lumped 6-8 9-10 11-12 and 13+ so sometimes my 1st yr L4 (6) would compete against 2nd yr 7's or 8's. This year they now have a Open (2nd yr) and Novice for 1st yr L4's. Not fair, LOL, that they did this a year too late for us. In our states meet they broke it down even more to age 6, jr7, Sr.7, Jr 8 and Sr 8, ect...because there were so many girls.
Try not to be too discouraged, you would be *shocked* at how well the little ones do against the bigger girls!