Cousin annoying my lifestyle

So my dad has his own computer business that he runs from home. My cousin wanted to learn off him so he comes here everyday to learn and help my dad. Thing is though, when he has nothing to do, or if he's taking a break he always comes into my room and lingers and ends up disrupting what I'm doing. I find it really frustrating. Like I'm trying to freelance so I'll be doing some research or trying to find clients or even editing some projects AMD he'll come and watch and yapping and it really distracts me. And then he'll even say "oi take a break" or "stop doing this" or "don't do this while I'm here". Like I really feel like telling him to shut up but he is a nice person.

I can't put my life on standstill or change my lifestyle. I like gaming in the evenings after I've finished my work and because it's so late when we have to drop him home, I can't even game cos either he makes my life come to a stand still or he'd play aswell and I can never play properly with my friends. What can I do. It's beyond frustrating but he's a nice guy and I can't shout or yell or say anything rude to him.

Also forgot to mention it is also affecting my routine. Normally I'm in bed by half 9 or half 10 and I wake up early like 5 or 6. But since he's been coming and everything in my day has been delayed, I'm doing everything later therefore I'm not going to bed at midnight and not waking until 8. I absolutely hate it. I like waking early

How old are you and how old is he?

The thing im most disturbed by is that you said you like waking up early! Seems like your cousin is lonely. Like hes not comfortable enough in your house to just go off and do what he wants to do and he just wants you there to make him more comfortable and have someone to chat with. Id say your options are to be brutal and say he cant interrupt work or just schedule in time for him

I'm 23 and hes 27.

I was very much expecting you to say he was 15 or so years younger. A 27 year old that doesn't have the awareness not to bother people when they're busy might need more than a firm talking to. Also discuss this with your dad. It's fine if your dad is working and takes responsibility for him, but it's not fine for him to interrupt you when you're working. If this were an office, it wouldn't be acceptable for him to go bothering other colleagues and it's no different just because you're family and working from home.

Not to sound rude, but does he have any mental health issues that could be impacting him? As this very much sounds like the behaviour of a young child rather than someone in their late 20s.

I'd honestly get a lock on the door. I've worked from home freelance since 2012, and people don't 'get' it. They come in for a chat, ask if I want to go out for lunch, ask me to run errands because I'm at home.. In the end I had to say look, just imagine I'm NOT at home, and I'm in an office until 5pm. Then, I'm all yours!