Hi,
Timelessness to me revolves mainly around the story. Settings and world build's change as time passes. So you could argue that Romeo and Juliet is dated by it's world - which of course it is. But then it got remade as West Side Story, showing that the underlying story still holds.
Having said that even stories can date, simply because the world we live in makes them impossible. For Romeo and Juliet imagine if in the next ten years or so internet policing etc became so effective that crime families / organizations could no longer exist. Then that tale would fast run out of meaning for the following generations.Cheers, Greg.