"The post-kayfabe age" is a strange title, admittedly, because almost *everything* is the post-kayfabe age.
Legendary shooter Frank Gotch wrestled shoot matches and worked worked matches, jabroni mark. The transition to the work in full developed in the early 20th century because pro wrestling was really rather boring - just endless methodical slogs - so quite why WWE has taken on the pacing of the 1910s 110 years later is rather puzzling. It's no wonder that they find it difficult to reach a young audience.
So realistically, all the great, all-time heat moments - Ole Anderson locking Dusty Rhodes in the cage, Terry Gordy slamming the cage door on Kerry Von Erich's head, Terry Funk drilling Ric Flair through a table - all transpired when the game was up.
But the millennial generation for whatever reason defines "post-kayfabe," generally, as the period of time when they stopped believing, whether that belief was shattered by Brian Pillman or Vince McMahon's open acknowledgement that the events of pro wrestling were all scripted.
So, for the purposes of clarification, the "post-kayfabe age" is defined here as "the years after thirty-somethings grew up and stopped reacting earnestly".
The paradigm shifted into a paradox. Wrestling fans respected those who managed to draw boos, because it meant they were great at their job.