Here are my experiences:
6th grade, pre-puberty: 9:5? mile
8th grade, post-puberty, no training: 7:06 mile
Freshman year HS, soccer training (10 MPW?): 6:07 mile
Sophomore year HS: didn't run
Junior year HS, 20 MPW: 5:30 mile
Senior year HS, 35 MPW: 4:58 mile
Freshman year college, 55 MPW: 4:03 1500
Sophomore year college, 70 MPW: ??? I'll find out by next year.
Are there any other people out here who started off slow but had significant improvements after training?