Following looks like it was made in the early 60's not 98-99

It's probably due to the low budget and the film used but the film really looked older than it was.

Also stylistic choices by Nolan to make it a b&w noir obviously.

It's interesting that films with the absence of cell phones and the internet can also make it seem dated.

I think Nolan said he used a Bolex (obviously he used sound film since nothing sounded overdubbed just natural) which would also age the film considerably also.

It's just that a lot of films you can see from 80 to 2000 if they use certain film either look fairly freshly new or really old depending.