This is a post from Dave Weaver (Founder of New England Catching Camp) over at discussfastpitch.com. He downloaded the info from the NFCA site. Take it for what you will.
Lots of discussion on what is ave pitch speed for fastballs at different ages. I downloaded the results from the 5 NFCA Administered Camps held in 2008.
NFCA Pennsbury Recruiting Camp, Yardley, Penn., June 12
NFCA Great Lakes Recruiting Camp, Toledo, Ohio, June 19
NFCA Colorado Sparkler Recruiting Camp, Westminster, Colo., June 30
NFCA Colorado Fireworks Recruiting Camp, Aurora, Colo., July 1
NFCA Elite College Showcase Recruiting Camp, Plano, Texas, July 24
Now I have no way of knowing if any of the pitchers went to more then one but here is how the numbers worked out.
633 different pitchers results were tallied from the 5 camps
Each pitcher had the speed of 2 fastballs recorded.
The data for 1266 recorded fastballs showed an average MPH for all 1266 pitches as 56.5MPH
123 girls had at least one pitch at 60mph or faster
63 girls had both pitches at 60 or faster
Maximum MPH was 66, thrown 3 times by 3 different girls
Not sure what would be the ave age of these 633 girls but seems likely they are at least sophomores in high school.