Everything about aerobic running is built up through your life, while speed is inherited. Those sprinters who say they "can't do distance" might have been really good distance runners had things played out differently. It really upsets me when high school runners and college runners say they aren't good enough and won't ever be great because they try really hard in practice but only run a sub-par time. To my knowledge, the best runners ever in high school peaked in high school or college and such. I trained myself by doing very strenuous workouts in high school because I wanted to be very fast when my body simply wasn't ready and had to mature more. Here are some of my times and I assure you I was running as best as I could:
9th:
5k - 17:23
1600 - 4:42
800 - 2:08
10th:
5k - 16:11
1600 - 4:31
800 - 1:58
11th:
5k - 15:43
1600 - 4:24
800 - 1:58
12th:
5k - 15:11
1600 - 4:15
800 - 1:56
Freshman:
5k - 14:46
1500 - 3:54
800 - 1:55
Sophmore:
5k - 14:11
1500 - 3:49
800 - 1:53
Junior:
5k - 13:55
1500 - 3:49
800 - 1:52
Senior:
5k - 13:52
1500 - 3:45
800 - 1:52
As you can see my progression was pretty linear but I either focused on speed or aerobics in some years. I still think my 800 time could have been a little bit better along with my 1500, but my 5k was what I was really good at. I ran DII but transferred to DI. In addition, I didn't peak until I was 28 years old and I finally graduated medical school so I was still in college and in that atmosphere. I didn't run any mile races or the such and I just did 5k runs on the track that I could get into. Here is my progression for those:
25 - 14:02
26: 13:49
27: 13:46
28: 13:42
It was basically just taking small steps to success. I currently have 13:42 as my PR but in college it was 13:52. A lot of people think they won't ever improve even as early as a sophmore or so in HS because they can't beat their friends in meets despite working harder. What I have to say is everybody develops differently. Both my parents and I weren't at our best at any sport until our very late 20's, and if you quit you will never know how great you can become.