Animal Care Needed - Now Hiring

I have a kitten that is 6+ months old and will not stop attacking my senior cat. My senior cat is so chill. But my kitten is so wild which I understand is expected hes a kitten. But every time we let him out he attacks. We keep him in a bathroom and sometimes a big dog cage (recommended by his vet) so he can watch our senior cat all day long. We have had him for 3 months and its no different.