When the golden age of TV started and stopped is all a matter of opinion.
When love scenes changed from kissing and suggestions of having sex to outright raunchy full nude sex scenes, that would be the end.
When language went from light weight cuss words like crap, turds, etc to F word being used in every other sentence, that’s when the golden age ended.
When TV started pushing leftist political agendas, that’s when the golden age ended.
When homos came out of the closet, that’s when the golden age ended.
When TV commercials became filled with political agendas and now wokeness, that’s when the golden age ended.
When cable TV (HBO & Showtime) went from first run movies right after the theater got them, but before they started producing their own trash, that’s when the golden age ended.
When the mainstream news channels went from occasional little white lies to outright full blown made up stories and other complete lies, that’s when the golden age ended.
I would say the beginning of the end would be the mid to late 90’s. Today the only TV worth watching is what is carefully selected from a streaming service that has no ads that one pays for.
It ended with media consolidation. You basically have two or three mega-corporations generating all the content, just more channels.