I have a 2nd-year 12 on our team and she throws consistent 55mph. She is CLEARLY the fastest we see in our area. We were in Fresno and I only was around to see a couple of 12's (Corona has one I think?) that throws harder. Not saying there aren't more, just didn't see 'em.
Now knowing she is mid 50's on a couple of different guns that various coaches and parents put on her, I chuckle when I see the girl on a team that her coach tells us can throw 60. Looms more like she's at 51-52... tops!
Now that being said, we had a 10u a couple years ago that was actually 9 and she was throwing 55, but with the smaller ball at 35', I don't count that the same. Still, she was really fun to watch! She's a 2nd yr 12u and throws about the same speed, just better movement now.