There's nothing wrong at all with it and please don't let anyone tell you there is. Last time I lived there, my 15 year cousin still slept in the room with his parents on weekends, just because he likes to spend time with them and not have to worry about getting up and going to his own bed. Poorer families share rooms/beds all the time and no harm has ever come from it...

Unless of course you need privacy for any reason, then he should respect that.