Are people in here aware his stature can actually be an advantage? You'd also do well to judge quadricep and core strength as with those, tiny players are infuriatingly difficult to play against, especially if they are cute enough to shield the ball correctly. He's a teenager; he will fill out and that's all that matters. What's to assess is: technique, speed of thought, reactionary intelligence and adaptability, confidence, movement, combination play etc. Hope he gets numerous chances from hereon in.