This is for the purpose of the point of course, but I think top 30 as a junior isn't to be scoffed at. If you think more than 12 miles for 60 miles a week isn't frivolous, I'm not sure what factual evidence you're looking at. If you're looking at a 14 mile long run when your other runs are much shorter, it'll be hard to hold a fast pace for that long, and the pace will inevitably slow. Half the argument against mileage as high as 60 a week in highschool is that miles become low quality, and a 14 mile long run proves it when it's too difficult to hold a long run pace for that long--the pace shouldn't feel like hell, but all the same it shouldn't be slow, and so 12 is a happy medium for 60 a week.
Source: I run 60 miles a week and have run more than 12 mile long runs on many occasions, to a consistent result of a crappy pace for the last several miles. I know no other highschoolers in my state, where the top runners know eachother, that do more than 13 miles for a long run.
Longer than 12 is a fine way to burn out.