I always revert back to this:
10U - pitching and catching contest
12U - add infield play
14U - faster and add outfield play
I find 13U to be difficult due to the fact that you need real outfielders. And to that point in a players development, they have been wrongly conditioned to believe that the best players play on the dirt. At 14U you must have very good athletes running around on the grass or you will not win much on Sunday. I also think that the speed of the game is much higher.
I think the jump to 14U is bigger than the jump to 12U. But I also think the biggest physical difference happens from 11U to 12U. The pure size difference is amazing.
I have one in 16U, 13U, and 12U. And I still like old 12U and 16U the best. You can take the 13U and 14U years. I find those years to be the hardest due to the players being difficult to manage and the parents having one last spin at being crazy. 16U and 18U both seem to be a much more enjoyable age group than the 14U years.
To answer specifically, how many pure 13U teams end up in the top 10 rankings? 1-2 per year maybe. The older girls are more consistent and take a much more mature approach to the game.
Actually, I prefer watching the 18U+ teams. The players drive themselves and are only there for the love of the game. It is actually the best. My DD picked up on a 19U team (1st year college players) and had a blast. The girls managed the playing time themselves and had fun. There was a head coach but he didn't do much other than roll out the lineup. The catcher and pitcher called the game and it was all run by the players. No parents yelling, no coaches yelling, just girls out there playing the game.