That is some serious natural talent. I would bet that if the sprints were his focus he would easily run sub 50s.
51.72 isn't bad for a kid who reportedly likes to put in the big training mileage.
1 Boys 400 Meter Run Var
Griffin Carter Valencia 50.25 50.25
hall chad Big Bear 51.72 1.47
Estrada Gus Arroyo 51.99 0.27
Opoku-Agyemang Joe Clovis 52.08 0.09
May Stephan Great Oak 52.48 0.4
Ferrell Kenny Redlands East Valley 52.78 0.3
Galvan Luke Whittier 54.18 1.4
http://www.dyestatcal.com/results/trk2007/March/24%20APU%20DMOC/Summary.htm