As fast as they can!
Depends on how fast they are
About 16 seconds for a slim semi-fast girl
faster than me
A 10 year old girl should pitch about 40-55mph.
probably about 15-20 seconds.
A 12 year old girl should be anywhere from 40-47mph.
Well back when I was 13 a ran a laser timed 6.8 years. But you might not be that fast; cause 6.8 years is pretty fast for a 13 year old!