Your mile is (just a little bit though) relatively the slowest of your times.
A 6:00 mile predicts:
20:50 5k
43:15 10k
1:36:26 half marathon
Of course predictions aren't right on.
This says to me that:
* You didn't do enough speed work for the mile race...OR
* You are much better at endurance than speed...OR
* You were more fit when you ran the races other than the mile
Some will insist that you just need to do some workouts to get that mile time down, and I agree that you can, but I know a few runners who just don't have the speed to run a decent mile but can do comparatively MUCH better as the distance gets longer. That's why we have several different distances to run.