I am a junior in HS and I run about a 17:05 in the 5k. Our coach has us run a pretty low amount of mileage. Our week generally consists of this:
Mon: 3x800s simulating 5k pace
Tue: 30 min run
Wen: 2 to 3 mile run followed by 100m strides
Thu: 30 min run followed 100m strides
Fri: 2 to 3 mile run
Sat: 5k race
I know this is pretty low mileage for a lot of people here. But our team is doing pretty good. Our fastest guy runs about a 16:30, I'm our second fastest runner at a 17:03, our third guy runs a 17:15 and basically all of our varsity squad is under 18.