Slow Mental Growth. He fibds to throw.

My 4 year old son had been going to Nursery school for one year but still he don't know how to even catch the pencil. He don't learn anything. He is aggressive and cry a lot for anything. He just lay on ground and start crying. He even don't eat except Potatoes and Roti , rice and Dal. He drink milk and Horlicks and like it. He don't eat vegetables. He seems no idea of what he is holding. While eating in plate , he throw it as if he is restarted. He starts beating other adult and children with anything he finds around. He don't even listen many time even if someone is saying it too loudly. For example , if he is holding pencil in hand and someone say him look at copy and write he do not listen and not even see the person who saying for writing. He just keep on looking in other direction and don't even look to the person. If someone forces or scold him , he become very aggressive and retaliate with whatever he fibds to throw .