Yes, don’t let Buddy into your room. He shouldn’t be eating Trouble’s food, he will get fat and you will be spending a lot more money on cat food than you should need to. Is Buddy fixed and is Trouble spayed? At five months, she is quite old enough to get pregnant and if Buddy hasn’t been neutered, he will make her pregnant. I find it hard to believe that a five month old female is beating up a year-old male but seeing that she is… The thing is, your room is Trouble’s only territory. It is the only place she has to feel safe and at home. Buddy has the whole blimmin’ property to roam over. Trouble needs her own territory to feel safe in and like it’s her own space, it’s not fair to let Buddy in as if he owns it. It’s good that Trouble is letting him know that it is her space but as Buddy gets older and bigger, he might start fighting back or getting aggressive towards Trouble. Think for a minute how you would have felt growing up if your mum let your older or younger brother run in and out of your bedroom just as if it was his, but also let him keep his own bedroom to himself. You would have nowhere to retreat to and relax and be your own person and do what you want to do without fear of sudden interruption or annoyance or disturbance. You would soon start stressing out. Don’t do that to Trouble.