can 7-yo boy have antisocial personality disorder?

My 7-year-old grandson appears to hate his little brother, who is 4 years old. He has continuously hit, punched, tripped, kicked and otherwise hurt his little brother since the brother was 2 weeks old, when he poked him in the stomach with the sharper end of a curtain rod. Although the baby cried at that time, he did not appear to have internal injury, based on no further problems or crying. My daughter and her husband are now trying to curb this violence as the younger brother is beginning to fee he is \"bad\" and should \"die\", based apparently on the fact that his older brother has been allowed to hurt him with little or no consequences for four years. The older brother appears to feel no remorse at all and nothing seems to get through to him that this behavior must stop. Any ideas? Help!

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