It's tough to give an average....but based on what I've seen (son is at a mid-major) at D1 and with the local D2's and D3's.
I'm assuming RHP....you can probably subtract 2-3 for a LHP
Again, these are just my observations based on kids I know playing at various levels
D1 Power 5.....90+ average
D1 Mid Major.....87-90
D2 85-88 and top guys a few more
D3 84-87....again, the top guys can be higher
JUCO and NAIA....really a huge variance from the top teams to the lower level teams. A local NAIA has 3 guys throwing 95+.....while another probably doesn't have anyone over 85. A pretty good JUCO nearby had guys from 84-90 with most in the 86-88 range.
My son has friends playing at several D1's in the midwest...all our sophomores this year
My son....mid major D1 90-91 last summer, 91-92 this spring
LHP at Power 5.....92-94
LHP at Power 5.....88-90
RHP at Mid Major 88-90
RHP at Mid Major 86-87 last spring
Hope this helps a little