People saying "he already trains like a pro" are outrageous. Sure doing workouts with such high level training partners is a nontrivial part of the equation. But have you seen the kids strava? Do you remember that until winter of this year he was an unheard of , unremarkable, 4:25ish runner who apparently excelled at rock climbing?
In terms of a performance to training ratio, Kessler seems like a good candidate for the most talented American high schooler ever seen. Ryun is of course legendary, but so was his training, and he excelled for several years in high school. Kessler has seemingly went from 4:2x 1600m to 3:34 1500m essentially overnight, and has no discernible training volume to justify any of it.
His strava is available. It's unclear if he logs everything there, but the last 12 weeks have mileage of 17miles at the lowest to 42 miles at the highest, probably averaging around 30-35mpw. That is an unthinkably miniscule amount of training, especially when you think he may have only been doing it for 6 months or a year, in which to develop the aerobic capacity for 3:34 and beyond.
From his strava, one can see that his easy runs are insignificant affairs sometimes reaching up to 45 to 55min, as "fast" as 7:15 pace or so. But more often 3-5 miles at 7:30-8:00. There is almost no discernible aerobic conditioning happening in his training outside of primary workouts. That is remarkable. Say what you will about hard days hard and easy days easy, but from Lydiard to Canova and everyone in between, the significance of aerobic conditioning using sustained aerobic running *for distance runners* is indisputable.
At any rate, he seems to have infinitely untapped potential. Imagine the kind of lifetime mileage and aerobic conditioning Jakob Ingebrigtsen had accumulated to reach similar (and so far better) performances at Kessler's age. Kessler has produced them within 6-12months of running probably less than 4 or 5 hours a week. Jakob probably spent double that time on the skis when he was 8 years old!
The only caveat is if Kessler is in fact a freakishly talented Brazier / Murphy type, who will never approach significant aerobic mileage in his career and instead focus on 800m / 1500m. His performances thus far at 800 vs 3200 lead me to believe he will end up a genuine distance runner, but i suppose only time will tell. NAU should be able to have him around 13:15 or much faster in his first year there.