Nobody is talking about haircuts when they use the word “dated” to describe something.
Nobody?
Ok.
In 50 years, do you think a Star Wars audience is going to be able to tell a 1970s haircut apart from a 1990s one? I don’t think so. I think these things are inconsequential unless they detract from the film, which of course it doesn’t. Luke’s hair doesn’t call attention to itself; it’s just there.
Style, whether it be costume design, or lighting, etc. has no impact on whether a film gets dated or looks timeless or not. Myopic creative vision does. When elements like the plot or the effects of the film render it only pertinent in its contemporary era, then a film will become dated when that era passes and subsequent generations find no use for watching it.