Man Overboard wrote:
In this particular instance I think the coach is right. A HS freshman should train for where the race times they realistically expect to hit in the near future, not based on past performance. For someone your age, I vote for "less mileage at a faster pace" for almost all of your runs. As others have said, if you want to throw in a long run every once in a while, by all means slow it down to 8 minute pace for that run. No problem.
Young runners get burned out, both physically and mentally, from running too much and/or too hard within effort ranges of their roughly 1500 to 10k race paces. A young runner doing 40-50 mpw at a controlled pace for the vast majority is going to be less likely to get hurt than someone pushing all their runs to the limit (which 7:00 for a 4 mile run would in this case) and doing half that volume.
The tricky part with young athletes is that their fitness is far more of a moving target, as things like growth spurts can sap their energy and coordination, while their novice status can conversely mean their current race fitness meaningfully improves on a weekly basis, where a more experienced athlete would take a full meso-cycle to move the needle half as much.
OP: I wouldn't even take a watch with you on runs for now, unless you're doing timed rather than mileage runs.
As another poster said, aim for 6 days a week, working up from 30 to 45 or so minutes on most of those days, at whatever pace you're comfortable with on that day.
1 Day per week go longer, aim to progress from 50-65 or so minutes.
1 Day per week do a warm-up, then do 5-6 x 50 meters as fast as you can, with as much rest as you want to make every one as fast as the first. Cool down 15+ minutes after.
1 Day per week, when you feel good, start off like you would on all your other runs, but after 15 minutes, start gradually picking up the pace until before the point where it would be a struggle to finish the run.