Is there a mental disorder that makes you more child-like?!

I have this 26 years old friend who has the mind of a 13 year old. He lives at home with his parents and has a room filled with anime posters, toys and video games. And when you speak to him he only talks about anime cartoons, tv, and games. He also has no job and is part time in school but he often skips to play video games. In conversation he rambles and seems overly friendly.... It's as if he had been locked in a cell by himself for 10 years... It's strange....He's not just a down on his luck babied guy.... I think there is something wrong with him. He doesn't even seem to be aware of his status in life.... He thinks the way he is and his life is normal.... Anyone have any idea if he has a diease of some kind? I know this could come across as a lazy loser type guy but he's not... If you met him you would know what I meant