Yes, I too feel it would be interesting to know of those who have become MLB pitchers what their velocities were when they were at 9 to 12 years old. Somehow, I get the feeling that there's not much correlation with high velocities at that younger age.
I remember when my son was in LL Majors and was throwing at 65 mph+ and watching the LLWS pitchers pitching 70 mph+ and thinking that my son was about or maybe a little above average for a 12 yr. old. In his HS Sophomore year he was touching 90 and sitting around sitting at 87-89. His Senior year he touched 93 and sitting around 90-91. Drafted out of HS as a pitcher but decided to go to school and in his Freshman college year he touched 94, but decided he's rather play a position than pitch and so he has.