Not to be pessimistic, but I also think that decreasing your mile time by 2 minutes is a huge feat. How about taking steps. Perhaps this year or in the first 6 months you can shave 30 seconds off and then next year or the next 6 months you can take off another 30 seconds. You may find that you are more successful that way. You may want to ask a coach for some help. Are you including a long run, a hill workout as well as a tempo and speed workout into your weekly running?
I have been a runner for over 25 years. In high school my mile PR was 5:37. I am in my 40's and right now I am in the low 6's, not too bad. However, endurance running is where I have excelled. As I matured, I learned how to treat my body better, which included fueling more efficiently as well as cross training and different types of running workouts.
I love setting goals. But, I am careful not to set too large of a goal without having the proper steps planned out (mini goals). Good luck and I hope you are successful!!!
Jen 41/ w CF (Delta F508 and R117H)