Dibble used to throw almost that fast, but they manage to light him up many times.....like Judgie said, its the offspeed stuff after the fastballs that gets him...he'll have to master an offspeed pitch as well....but with talent like that, he probably has/can....
Major leaguers can hit a 120 mph fastball if there's no movement and they can sit on it. The really interesting thing, as everyone has noted, will be seeing what he has to go along with that heat. At least I know I'll be interested in getting a look at his stuff.
I highly doubt anyone can hit a 120mph fastball. The reaction time on 120mph would be like .3secs. While at a 100 its about half a sec. Just making contact and putting the ball in the field of play would be quite an accomplishment. Have you ever tried hitting a 75mph pitch and then step into a box facing 90? That extra 15mph makes a world of difference.