Sounds for the most part like the appeal to novelty logical fallacy, or argumentum ad novitatem.
However, there's a fine distinction to consider. The appeal to novelty represents a prejudice in favor of the recent or the new. "It is more modern, ergo it is superior."
What you describe is a complementary prejudice against the past: "It is old, ergo it is inferior."
I also considered chronocentrism, but that again does not quite capture your full meaning. That denotes the assumption that one's own times are the most important and relevant in history.
Again, finely interpreted it is a bias in favor of the present, not against the past.
When speaking of people, ageism would be appropriate, but when speaking of ideas it is not correct.
I'm still pondering a proper fit. Perhaps these suggestions will steer one of us in the right direction.