I think the focus on his weight is fool's gold.
For the average population 5'7 160lbs is not fat.
You're asking this dude to lose 20lbs at 5'7'...that is a ton of weight.
As a comparison when I was running my best I was 5'5.5", 143lbs. Ran 4:27, 9:32, 15:47, 1:09:40, 2:32:40. Did skinnier runners beat me? Sure. Did I beat skinnier runners? Yes. Was weight the reason? Not at all.
Without seeing what this guy actually looks like we can not make the determination that he needs to lose weight.
What he needs to do is train. Train TRAIN.
20-25 miles is nothing. He's been "running" for 2+ years and only putting in 20-25 miles.
I stick with my key points in order of IMPORTANCE.
#1: Train. Put in miles. Hit the pavement or trails. Run more. Run more farther. Run more faster. Take 1 day of complete recovery...you're 27 not 17.
#2: Run fast. A mile is short by distance standards. You need some interval based speed training.
#3: Endurance. Tempo runs. It's easy to run long. It's easy to run fast. It's harder to run moderately fast for a moderate distance.
#4: Overall conditioning and strength. Strength will keep you in it longer without getting hurt. Strength, without added muscle, will ensure you get the most out of every muscle contraction.
Alan