Me and my brother are roughly the same as age, I'm almost 20 and he's 18, and he is about as immature as a 16 year old. He thinks he's entitled to everything and always has to get his way and I don't know how to stop it without resorting to violence.

For example, today he walks into the living room wearing my shorts which isn't a big deal but when I pointed it out he claimed they were his shorts when me and him both know they are mine. Then he told me to quit whining about and said I was acting like a baby. This kind of situation happens weekly. He thinks he can take my stuff without permission and after 18 years of it I'm getting tired of it. I'll have to live with him for 2 more years so I need to find a way to put a stop to it. Any suggestions without resorting to me kicking his ass?