I'll give you some perspective...from my personal database...some are students of mine, some are girls I've used pocket radar on at local\regional\national tournaments.
9U Pitchers: High: 44; Median 35
10U Pitchers High 49; Median 41
11U Pitchers High: 51; Median 45
12U Pitchers: High: 53; Median 46
13U Pitchers: High 56; Median 46
14U Pitchers: High: 60; Median 50
I don't use "mean" because some girls get radar-itis when I bring out the radar. Also, some girls have 100 pitches tracked and others have 20...
At 10U I could care less about spin rate...you're 35 feet away...speed (should) over come spin at that distance..spin becomes more relevant at 14U as their movement pitches become more important as hitters improve.
My 2 cents...CP
I always tend to under state my DD's speed - I prefer to under promise/over deliver, but it has always been amusing listening to parents with rose colored glasses pull numbers out of their keister.
Had a parent in DD's organization (at 12U) tell me her DD hasn't thrown a pitch under 50 mph in months. I pull out the pocket radar and clocked 47 mph 3 times. Response: "My radar gun isn't right."