AITA? --I don't want my little brother in our shared room when I'm not home.

This is more of a rant than really asking AIO, but I want some unbiased opinions on this topic, because I feel like it's not discussed enough. This is technically my throaway/lurker account, and all mentioned/relevant people will be refered to by age so I don't confuse names. There's also a bit of context so this may get long, I'll add a TLDR at the end for those who don't want to read :)

Now, before anyone jumps to conclusions, I know how the title sounds, but please let me explain.

I (20) currently live at home with my parents while I finish college, which I am about a semester away from graduating. The house is only 3 bedrooms and there are 6 people living here as of now. My 3 siblings and I have the 2 smaller bedrooms. My sister (22) and the older of the boys (18) share a room, and I (20) and the youngest boy (7) share a room.

The thing is, my youngest brother has developed a bad case of sticky fingers over the past year or so. The space in our room is split fairly, for the majority, and I try to keep my things to one of three places; on/in/under my desk, on/under my bed, and on my shelf, which is tucked into the corner of the room.

I'm a bit particular about my things, as I'm both an artist and a collector, and much of my stuff is valuable, both monetarily and sentimentally. I have told (7) multiple times, both firmly and patiently, to please not touch my things without permission, and if he asks, I usually don't say 'no' without a good reason. But he doesn't care. I've had multiple instances where he's snuck into our shared room while I wasn't home to rumage through the things on and around my desk without asking. He's taken art markers, my biking mask, my beats headphones, (which were about $130 roughly and where missing for 2 days because he took them to school with him) my lighters, matches, and multiple other items, some of which he took to school and got in trouble for.

I've have, and still do, express my frustrations about this with my parents, insisting that they please do something, because the situation is only escalating. My mom has told me to be patient, that she's trying to get him to understand that it's not okay to take other people's things. I had to get a lockbox with money from my own income which I've hidden under my bed with a combination. My dad is insistant with the opinion that (7) only takes my things because he's curious, and if I just showed him my stuff, it wouldn't be a problem.

The thing is, (7) is not, at all, being disiplined for stealing other people's things. It's not just my stuff, either. My sister (22) now keeps her Nintendo Switch in her room because (7) also tried to (or may have) taken it to school with him.

I understand that young kids sometimes go through stages like this. I had my record of sticky finger incidents when I was younger too, but I also recieved consequences and eventually got the message that stealing/shoplifting could ruin my life if I kept doing it. (7) Is recieving no consequences whatsoever. My parents don't believe in spanking, which I get, but they don't ground, confiscate, or punish (7) at all! The most I've seen is a frankly gentle "stern talking to" from my mom. But my dad won't do anything! I keep having to pack away, hide, or straight up get rid of my things to keep them out of (7)'s reach.

The whole situation is being framed as if it's my fault my brother is taking things, and even after mom and I agreed (7) didn't need to be unsupervised in our room with my things, my dad didn't give a flying damn! We got intoam a huge arguement about it. A lot of things went back and forth, and he basically threw mom's rule to the wind and told me "tough shit, it's his room too, he has a right to be there. if you don't like it, then leave." This is beyond infuriating now. I feel like I shouldn't have to hid my things, valuable or not just because niether of them with actually give (7) the consequenses to his actions. As a side note, (7) is also destructive, especially when he doesn't get his way. He's ripped up multiple posters and art works of mine that I had hanging on my side of the room, and that was basically an "oh well" too.

I really need some opinions here. Am I really overreacting over this, or is my frustration justified? I just really need some unbiased opinions and advise...