Cat depression/anger?

Dex was taken away from his litter over a month too early. Kittens that stay with their litter until 10-12 weeks are more well behaved because they learn how to play with their siblings, and are better kittens for it. Your kitten just doesn't know that what he is doing is wrong. Is it possible for you to adopt a second kitten, one that Dex can learn how to play properly with? This isn't always possible, but its a very good solution. Otherwise, you will need to be his litter mate. If he plays violently, just walk away. He is looking for attention, and even negative attention gives him what he wants. Ignoring him when hes being bad, and rewarding him when hes being good, is the best way to train him.