I don't really understand how or why some of you are relating physical size to agressiveness. As a coach, if I am telling a player I want he or she to play more agressively, it means I want them to pick up the intensity level, put in that second effort, fight harder for the puck, be stronger in the corners, fight harder through checks and check harder in the defensive end. Its particularly important for a player who is trying to make a team of players older than him. Take Sidney Crosbey for example playing with players older than him (both in the Q and world juniors). He is a very aggressive player.
I am looking for some guidance or suggestions from anyone creditable to this specific training.
It will be important for him to be prepared to play with players who are physically bigger, but as I've said, being big and strong doesn't make you aggressive. I would also be wary of doing extensive weight programs at very young ages.
My Interpretation of aggressive is maybe different than some of the rest of you, if so thats just a difference of opinion I guess. Theo Fleury, Doug Gilmour are just two examples of players who are small but agressive. You don't need to be built like a power forward.