Please could someone tell me when its ilegal for a boy and girl sharing a room as I've been told two different ages by the same council

Don't know where you live (council?) but in the US it is not 'illegal' to have opposite sex children share the same room... when children reach a certain age I would imagine that parents would not want them sharing a room, I would even say that at a certain age they should not share a room, but it is not 'illegal'. (just to let you know, I have no law experience, but I'm sure of this one)