In the offseason, when I'm going 6 hours a week (average high schooler here) it takes about 4 or 5 months to wear pretty bad. I get smoothed out on the inner front part of the sole, so that the white shows through. The entire top half is smooth, and the edges are worn through. The back half (swoosh area) is totally fine, and then the outer back edge (where it says Zoom Vapor) is usually worn down. I've started to toe drag and that has hurt the front a bit more...
During the season, in the Spring, I get a little less time (10-12 hours a week) to run through them, maybe 2-3 months.