Running a half marathon takes a lot of practice and dedication, so an average time depends on how long the participant has been running and training for the event. For a professional runner, a time under 1 hour and 12 minutes is considered excellent. For an amateur runner, a time that comes in at around 2 hours (or about 9 minutes per mile) is an accomplishment.
While a runner can train for a half marathon, they can never get a feel a specific course unless they run it first. Factors like hills, temperature and the number of other runners on the course often make average half marathon times increase.