One thing I noticed about this site is that if someone does something impressive, 70% of the post will have something to be overly negative about. Give the kid his props. At 20 years, consider his present and future potential. If you want a strict, by the book bench, than go to the nearest "Health Spas" and have Biff, the foo foo toned 150lb PT, show you how to do a proper flat bench chest press.
The kids using 400lbs for 10 and I wonder how many guys here can squat, or even DL, with that kind of weight? Let alone get 500lbs up. And if they were true about their lifts, how many could bench 300 in half way decent style for 10 reps. That kids just born to be a bencher's, as some to be squaters or DL'ers. That is the luck of the genetic draw. My two cousins (17 & 18 at the time...both weighted in the 220 range), BP's in the low 400's for reps in regular workouts. For them, it was not that big of a deal.