It depends entirely on what weight of BB was used to determine the 460fps really. I once won a GSG522 that claimed 450fps on the box... with a .12g BB.
I highly doubt landwarrior have actually chronographed the gun, it's far more likely they've just copied the manufacturer's data sheet.
Can't go far wrong with either of those and if your son is still young, makes sense for him to have a more CQB style RIF as they can get heavy, quickly.
Can't go far wrong with G&G or Ares, so it's really down to personal preference? You'll end up spending more than you thought once you're faced with all those lovely RIFs though - and besides, one is never enough ;)