My son was hitting 68 mph before he turned 12. 2 months after his 12th he broke 70. There were 4 kids in his 12u division in his league that threw harder. 2 threw over 70 mph, the other 2 were over 75. One of them is now Robert Stock's teammate at USC. Speaking of Robert he was throwing 80 mph as a 12 year old and now is mid 90's. His brother, still in high school, is said to be throwing over 90 mph.
My son says he was clocked at 87 mph. I don't know if he throws that hard, but when he recently nailed a batter with a fastball, we all felt that batter's pain. He had retired 7 straight with 4 strikeouts prior to nailing the batter.