So don't set an expectation for yourself that you might not be able to hit. Depends a lot on age too.
But just start running and work on getting faster each time! A few tips:
- try trail running. That made me faster on flat surfaces too, which was surprising. It's just a good workout.
- do some intervals where you try to go race pace for 400, 800, 1200 or 1600 meters.