Personally I was diagnosed at 18. I think usually people are in their teens/early 20s when they develop it. I DID know a girl that was diagnosed with CFRD at age 8 though, and that was quite a long time ago (I was only about 9 myself).
Sorry I can't offer much more than that. Yes, the average age is probably older than your daughter is right now, but if she has it, she has it, and it is best she gets the treatment for it right away. If she does turn out to have CFRD there is a wealth of information and support for you here, SaltyandSweet probably being the in-house expert, along with a few others. <img src="i/expressions/face-icon-small-wink.gif" border="0">
Good luck, and I'll keep my fingers crossed that the test is normal this time.