Hasn’t pro wrestling always had guys in their late 30s-early 40s at the top of the card. It’s never really been a young man’s game consistently. The problem now is that there are no stars of any age range that aren’t part timers. Roman Lesnar Punk and Cena will be gone in a couple years.
There’s no stars left after that regardless of their age.
I feel it's just a case of people lashing out because they don't like the product anymore. 18 to 24 months ago everything was clicking for WWE and people could've cared less about very late 30s to mid 40s wrestler on the spotlight.
But when the product is stale, the first thing you look for is fresh idea and fresh(er) people on top to inject a spark. And WWE has historically been pretty adamant when it comes to doing a change of guard. Every decade you get 4 to 6 wrestlers that eventually get on top and it seems that currently, people want that process to start happening and it doesn't look like it will start anytime soon.
One of the reasons the Nexus angle got such an instant was because WWE had spent all of 08', 09' and 10' pushing the same people (with 08' being a pretty good year compared to the rest) and Nexus had 8 new faces to the WWE audience. Granted, most of them weren't ready for that opportunity and most of them were only midcard talent at best, but it was a clear sign of things to come with The Shield, The Wyatt Family and the NXT crew (Owens, Zayn, etc.) debuting and getting important roles in the 5 years after the Nexus stuff.