For me, the Golden Age ends when the comic code begins, which is generally what everyone goes by.
*shrug*... As far as modern, it's 85+ according to plenty of shops, comic sites including this very one, wikipedia if you consider it a valid source.
I think 92+ is better, but it's obviously well past it's due date. It needs to end, and be re-named, so a new era can begin... but what do you base the end of the current era on? The end of the bubble in the early 2000s? Just make it an even 20yrs? The start of CGC, and first X-Men film in 2000? The beginning of the MCU in 2008? People come up with all kinds of reasons, who knows