In high school, I ran 2 seasons of indoor track (4:40 1600 and 10:18 3200.)and ran road races throughout the year from sophomore year. I played soccer year round for school and club, so my run training was all soccer training. I ran a 1:15:01 half marathon my senior year.
I went into the Army, played club soccer and ran for the unit Army 10 miler team twice in the early 90's ( mid 55 low 56 minute range. Pretty sure about the 55 minute part). Ran a 9:00 2 mile during a PT test, but the course had to be short. Probably by 200-300 meters.
During college, I partied and ran road races, independently, in the mid to high 15 minute range for 5k with minimal training. Still played club and intramural soccer, but at 5'3" didn't believe I was able to play intercollegiate level. Also, didn't really like (my perception of) the cliche nature of the cross country team.
Sporadic racing, and almost no run training, in my late 20's and 30's.
Didn't really start running seriously until a torn ACL ruined my soccer days at the age of 36.
Couple years later got my sh- stuff together, moved to Korea and started training to run. Since age 40: 15:45 5k, 33:19 10k, 1:14:34 half and an injury marred 2:53:53 marathon; all PRs.
This makes me competitive for overall and age group honors where I live.
At 42, looking to up my mileage and intensity to go low 32 for 10k, low 70 minute half and sub 2:37:19 for the marathon.
I am currently around 50 miles a week.
Hope this is an example you were looking for. If not sorry for the nostalgic ramble.