I would wager the 40’s measured at the NFL combine are extremely more accurate & less subject to manipulations than any 40 time at any HS camp anywhere. Football players get slower? Unless you don’t allow them to recuperate from the toll a season puts on them, I don’t think that is the case. Some HS athletes change positions & put on more weight to do so. Yeah, that could make one slower. An OL showing a 40 of 4.75 in HS then runs 5.3 in combine or college? That HS 40 was bogus, unless during that time he had a major injury.