I'm going to disagree. I think the late 70s and early 80s were.
I'm sure everyone who is deeply into something at the time it is happening feels it is the "golden age".
I'm 32 and have been reading fantasy since I was 8 - and for as long as I've been reading there have been good fantasy novels. I only caught the tale end of the era I'm talking about.
While tastes have changed I honestly don't think today's fantasy novels are any more numerous or successful (financially or critically) as other decades of fantasy output. I often hear arguments how modern fantasy novels are better written, or more complex, more grown up than their 70s, 80s and 90s counterparts - and while I agree on the current popularity of 18 rated fantasy, that is not the same thing as better written or more complex in my opinion.
It's just a different kind of complex.
New tropes/tastes rise, become stale and then become unpopular and that shifts the subjective mass of what people view as "good".
What has happened is fantasy has spread out into more sub genres, mixed and influenced by other genres. Gritty fantasy very reminiscent of 60s through 80s dark military/historical drama in a fantasy world. You'd find those books often set in vietnam or world war written by authors who had served or their fathers had.
Game of thrones on the other hand is very much a medieval historical drama - frankly it has more influence from shakespeare's historical plays than it does fantasy in my opinion.
Now authors are experimenting mixing fantasy with other genres of fiction and that's great, but I think it is easy for people to forget - especially people who didn't live it that all that "cheesy 70/80s fantasy" was just as new, wonderful and refreshing back then as gritty political violent fantasy is now.
Epic heroic fantasy was a rebellion away from the dark zeitgeist of the 70s/80s - especially in horror, and science fiction.
Personally I think the 70s and 80s were the golden age of fantasy, through novels, games (wargames, tabletop pen and paper and CRPG) it was the populist explosion of the genre. Made fantasy authors household names, created entire communities of people dedicated to fantasy worlds and storytelling in them.
fantasy authors were selling posters, getting featured on metal album covers, and having huge influence on TV and film. Much in the way comic books are having on TV and film today.
There was a dip in the late 90s I think, as most of the classic series ended, and the old authors often failed to deliver with their follow up works (with a few notable exceptions).
So without a doubt fantasy is going through a refreshing upbeat in novels right now (and a single TV show), it's certainly grown as a genre and it's tastes have matured as it's readers have matured.
But for sheer cultural impact and popularity, the 70s and early 80s were the golden age of fantasy.