My 9th-grader dropped 40 seconds in 4 months from indoor to outdoor -- from 5:40 to 5:00. So 4:10 is a long way off, but I'm guessing that 4:20 is within his reach in a few years, based on his trajectory and his enviable genetic profile
and for me, 4:40 (start sophomore) to 4:24 (finish sophomore) ... shaved 16s in one season for the 1600 meters. A number of factors contributed (none of which were weekly mileage related), but the point is relatively significant increases in performance shouldn't be dismissed. I only achieved 4:17 by my senior year, but that's primarily because I was fully committed to the 400/800 meters instead (50.4 & 1:54.x on 26-28 miles/week), and my mile participation was typically relegated to collecting points and not PR's.