I had a friend of mine who was throwing around 65 MPH at 10 years old. He was a tall kid for that age group and had long arms which helped his velocity. I was the catcher for him, and while he struggled with control, that type of speed is rare at that age.
Sadly, he never did anything after that year with baseball, nor any other sport. He didn't have anyone to really push him and its a shame because of what he showed that year. He's my age, and is struggling to make a living due to assault charges and drug possession charges that have really crippled his chance at getting a job.