I'm 18.
My PRs in HS went as followed:
9: 5:05 mile
10: 19:30 5k, 18:35 3 mile, 4:58 mile
11: 17:46 3 mile, 17:50 5k (This was probably short). Never broke 5. Around 11 for a two mile (don't remember)
12: 18:00 5k, 4:53 mile, 10:41 2 mile
Never ran a decent 5k at all (one time under 18? And I don't think that course was legit). In track I started improving a bit, relative to the past. I was never very good. But I liked the sport.
All those years it was pretty much 25-35 miles a week, and 35 was a high week. Running 6 days a week.
I had finished indoor track with the 10:41 2 mile PR. I never PRed again? Why? Too much speed work in the winter, and never had the endurance to carry me through anything. I finished my high school career, and I just loved to run so I decided not to quit, even if I wasn't going to be good enough to run for the University I'm at, but I decided to start logging miles.
Started out at 40, worked up to 70 by 5 a week. Every 3rd week I dropped back a bit. This was all really slow running, an occasional tempo run thrown in.
Within 1 month of just 45-55 miles a week, I ran a 10k PR, breaking 18 on the last 5k. Just a small dose of more mileage relative to the past, and I basically PRed in the 5k on the way home from a 10k. I was not prepared for this race at all.
A month of 50-60 mile weeks or so later, I ran a 5k. Still just slow running. PRed 17:35.
About a month and a half later of 60-75 mpw, I ran a hilly 10 miler in the heat. 62:40 or so. Not a blistering fast time, but it's a testament for more mileage, considering before the summer I never ran 10 miles under 70 minutes before.
I went to college, dropped the mileage a bit. I ran a couple XC races, one I had calf problems so it didn't work out. The next was an 8k. Times weren't too fast.
I ran a 5 mile road race recently. 28:32. I went through 3 miles in under 17, probablyhit 5k in right around my current PR.
Since going to college I was running around 50-55 mpw on average. No double runs.
Compared to most the people on this board, I'm slow. And I will admit that. But I changed my program to more miles, less anaerobic, painful intervals and I've gone from not being able to run 5 miles in under 31, to 28:32 in about 4-5 months. I hardly run any speed work, some longer intervals every once in a while. I've done a lot of my old workouts, not as hard, and PRed in them.
I plan on running 70-90 a week this winter, with double days, and improving some more.
I still have a long way to go, but without just putting the time in on my feet (and this is low mileage compared to most people on here--but high relative to my past), I have felt great improvements.