I've been a very strong runner all of my life. I jus finished my second year of college and have lost 2:30 on my mile and more than 8 minutes on my 5 mile. My PR is 4:35 for the mile and a high 27 minutes in the 5 mile. My question is why would it be so hard to get back in running shape? I realize that the college life has put a big strain on my overall shape, but I've been running 40+ miles a week for a couple months and my times are nothing close to where they should be. Do I just need more time to get that back? My Physical Therapist told me that I was in my prime and my times will never be the same because of age. but im only 20. could I already be out of my prime? any feedback would be apreciated. thanks.

To get fast you have to practice fast. You need to do some interval work for speed. You might also need some work on your strength.

You might not be pushing yourself hard enough. You could have more stress and be thinking about class, women and beer while your running instead of just running. I dont personally use a heart rate monitor but a lot of endurance athletes like training with them to make sure they are working hard enough. Also train aon a varried terrain then test your speed somewhere flat. youll feel great about yourself
my .02