What is comparative and superlative of old-fashioned?

"Old-fashioned" is already in the superlative degree. It means "most old-fashioned".

There is no comparative form of "old-fashioned" in standard English. However, you could use "more old-fashioned" if you are trying to emphasize a difference in degree.

For example:

* "Her dress was old-fashioned, but her grandmother's was even more old-fashioned."