My hs 1600 = 4:29 400 = 52split
College mile = 3:59.27 3 x 400 in practice afap w/5 min jog recov = 49-50-51
What made the difference for me? 30-35 mpw/CC in hs
70-100 mpw/CC in college. I was not overtrained in hs for sure and brought along slowly with steady increase in mileage and intensities over 4 years. Very fortunate to have only a couple minor injuries. I grew 3 inches between my senior year and freshman year track seasons so I was a late bloomer.
Decades later, I've seen many hs kids run way too much in hs and leave little room for improvement when they physically, mentally and emotionally mature because their expectations for themselves were too high coming out of high school. A good college coach will make sure the recruit does not fit this description and can recognize talent that isn't tapped out.
So, I don't think there is a solid answer for the original inquiry due to many of the variables I've mentioned. Obviously, I was an extreme example but had a great time surpassing many who were ahead of me in high school. Of the kids I've coached that have run between 4:12 & 4:17 in hs, while all have improved, none have gone on to break 4 minutes. I've always made sure I don't overtrain them to help them have that chance.