Here's some progress and regress of a long time runner; started running freshman year of college, at 18-19. I've thrown in some mileage stats for good measure.
19 - 36 high for xc, but 27:20s for 5 mile road
20 - 32:50 (70 mpw)
22 - 32:48 (70 - 90 mpw, just before moving into 100s)
25 - 31:48 (70 - 80 mpw)
27 - 32:09 (50 mpw)
28 to 32 - lots of sub 32:30s
33 - 32:11 (40-50 mpw, 5k type training)
34 - 32:31 (the slide begins!)
35 - 33:30
36 - 34:07
37 - 34:30s
38 - 35:30s
39 - 35:44
40 - 34:07 (masters comeback; 50 mpw)
41 - 34:20
42 - 34:40s
43 - 36:30 (crashing again!)
44 - injured
45 - injured
46 - 36:40
47 - 35:22 (60 - 70 mpw)
48 - 35:32 (60 - 70 mpw)
49 - 36:57 (30 mpw)(injured, but worked back into low-sub 36 shape later in year)