The eras as defined by wwe are always a little off. Attitude era officially started with austin winning the title, in reality Shawn Michaels going full dick mode kicked off the change in tone.
Here is my timeline for the eras
Golden Age/Hogan
- When Hogan pins Shiek - till 92 when Bret wins titles.
At this point most of the big 80s stars are gone and there is a passing of the guard with Savage and Flair getting phased out
New Generation
- Bret's title win in 92 - KotR 96 Austin 3:16 speach. That kicked things off into high gear. 96 was when shit started getting real. Remember Brian Pillmans gun? That ain't no New Generation era. That's Attitude and it was 96. Late 95-96 you can see the transitional change.
Attitude
-96-2002. Though some will say it ended with the Invasion and others say when it turned WWE. Both are good arguments. The format never really changed much between 2001/2002
Ruthless Aggression
2002- whenever PG kicked in. Still had somewhat edgy content with a stacked roster in the early years.