the average is around (72 or 73)
72-73..?? That is the average for 13-14 yo old travel teams in So Calif.. Most of the top 12 yo's throw low 70s... around here.
So I guess it really depends on the area.
The top P on most HS teams in our area throw upper 80s or more. And the slowest is throwing at least 79-80. Plus if you are throwing low 80s you better have great control and some other pitch or you will get hammered.
I estimate the average in So Cal for Varsity pitchers is 84-85. And there are very few if any that can't throw at least 80.
Now for the question of ELITE pitchers at each grade level... Remember San Diego has produced recent Pitchers such as Prior and Zito. But My son's high school runs a summer camp for JR HIGH age and incoming Freshman. Each session they clock every ones throwing velocity from the mound. They keep track of the best players over the last 12-13 years. So for players in the summer between their 8th and 9th grade... The top figure was 84 mph and 12 players that age have thrown 80 mph or better.
I would then estimate adding 2-3 MPH per year from there. With the top few ELITE seniors being able to throw low to mid 90s. Last year SD had Adam Jones throwing 95 and there will be at least a few more this year throwing low 90s