On the Sunday two weeks from today, I ran and walked 12 miles for 2 hours and 19 minutes. Last Sunday, I ran 6 miles for about 55 minutes.
When I started runing years ago, my co-worker who was a vet Marathon runner told that I could run 5 miles I would be able to run forever. Therefore I believe you have a very good start already. You should be able to finish a H.M. course with easy after a of months of training.
Way to go!