My best friend in high school had a crazy progression in-between his first cross season and second/third, then didn't really improve the last year of high school. And he made that huge improvement between freshman year and sophomore/junior year on only 45ish miles a week. Not really sure why he kind of plateaued because we ran all of our mileage together so I knew he was doing all the training year-round.
2014 -- 19:45 (standout race; much faster than other times that season)
2015 -- 17:38 (consistent times during season)
2016 -- 16:14 (consistent times during season)
2017 -- 16:56 (a bit better showing than most of the season)