I don't really know why he is still playing juniors at all....
Winning all four junior Grand Slams in one year would've been an amazing feat. And I guess he played doubles as well as he was going to be there anyway.
Even though he can no longer win the junior Grand Slam, I don't think Wimbledon juniors is such a bad idea either. The grass season is so short so he might as well gain experience on the surface while he can.
As for the boys' US Open event, well I don't see much reason to play it.