Board Size for my son

Hello,

I am trying to purchase a snowboard for my son for Christmas. He is 15 and a little short. He is 5'6 and weighs 122 pds. He does play water polo and is pretty strong. His skill level is intermediate to advanced. He likes riding all mountain, but is beginning to do some freestyle and park riding. We have been researching boards and we are having a difficult time finding a board that is under 151. We have been looking at the Never Summer Proto Ct and the Never Summer SL. We have also been looking at the Gnu Rider's Choice. The shortest size for these boards are 151-152. The Gnu Riders Choice has a weight range from 100-160 (or 170). I understand that Never Summer does not post a sizing chart, but that EVO has created one for these boards. The range for the 151 and 152 NS boards we are looking at is 110-160.   I am concerned that the boards may be too long for him. Can you advise? Thanks!!!