What the wrote:
Hate to break it to you but if the kid can't run at least 53 off no training then he isn't a sprinter. Even I could run a 54 mid and I was a slow long distance kid. Stop trying to turn distance runner into a sprinter. Put some 40 mile weeks in him and see what he can do in the longer events.
This is ridiculous. Sprinters do make progressions, and I'd not expect someone to run close to a (future) lifetime best in the 400 in their first half season.
I tried looking up the high school 400s of some top US sprinters, sub-45 guys, just to see what they ran in high school:
Tony McQuay's (44.35 PR) season best as a 10th grader was 50.96 - meaning he ran slower than that in all his other meets as a 10th grader and earlier.
David Verburg's (44.41 PR) season best as an 11th grader was 50.10.
Wil London's (44.47 PR) season best in 9th grade was 57.70, before going 50.54 in 10th grade...