Sub 16 3 mile on 40mpw?

yes, it would help

Why limit yourself to 40? The more miles you run over the summer the faster you'll race in cross country. It's a direct relationship. Build the aerobic base first, all other "trainings" are just details. The average runner makes the greatest gains just by running more.

Your 800 feels like your best event so far, although admittedly you have never trained for distance it would seem. Just don't get injured. I like 40 per week/ 50 max for you.

No, of course it’s not. At some point more miles will leave him burned out, exhausted or injured, unable to reap the benefits of the stimulus or incapable of doing any quality running. That point might be relatively low considering his previous mileage history. 40 mpw seems reasonable, going to 50 if he’s feeling good and seeing benefits.

Not if you build it up correctly. I have seen +5 every other week as the safest way to build of mileage with no injuries.

Really? Pros don't do 500 MPW. Most don't do 100 MPW.

If you're doing 20-25 then try 30-35, not 40.

Maybe stay at 20-25 but add a few hours of cross training.

You sound like a great candidate to get under 16:00, I think a perfectly executed summer could get you closer to 15:00 than 16:00 in all optimistic honesty.

I’d do 1-2 lighter workouts per week and have a down week every 4th week this summer, and start making the workouts a bit harder 3 weeks out from your first race. Your weekly mileage could look something like this for the summer early fall:

25

27.5

30

25 (down only easy running and strides)

32

34

36

30 (down, only easy running and strides)

38

40

42

35 (down, only easy running and strides)

40

42

45 (peak)

35 (down, only easy running and strides)

Workouts could be something like 12x400m working from goal 5k pace to goal 3200m pace with moderate rest, 3-6 miles at 5:50-6:10 pace, distance increasing as you get fitter, 6-8x200m working from mile to 800m pace with plenty of rest, 6x800m at 5:20-5:40 pace w/ very short rest.

With those 800/mile times, it should be no problem. 40 miles a week is fine, but miles per week isn’t a very good training metric overall.

Ill speak for them. Most pros aren't high schoolers on 25 mpw wanting to increase to shave 60 seconds off in a year. In high school it seems like that is pretty safe.

Well high schoolers couple decades ago would do that 100 mpw and they would smoke all these top athletes in super shoes.

Make sure you have a good nutritious diet. I ran 16:09 3 miles XC on a hilly course in pouring rain just after high school on zero (0) miles training (7 months of no running) because I was finally eating well.