if you're inclined to believe that fantasy fiction (for example) has been ruined since the late 1970s/early 1980s by the influx of Tolkien imitators, people who take Dungeons & Dragons as the baseline assumption of the fantasy genre, and (eventually) the rise of shallow grimdarkery as the dominant mode, then you're likely to see the golden age of fantasy as being at some point between the 1930s and 1960s, despite the fact that genre fiction didn't get much critical cred at the time. As said in my first comment, there's nothing which ties the golden age of criticism to the golden age of the subject of that criticism (assuming the term "golden age" is even remotely useful, which this conversation makes me doubt).
Emphasis mine, and in fact I would argue the two ages cannot be congruent for one simple reason: it's only really possible to understand such things in retrospect, not as they're unfolding around you. ("The owl of Minerva flies at dusk," as someone else once said: you can only fully understand something after it's over.)
It's easier to see now that Tolkien's work was not intended to give rise to a whole section of the fantasy shelf on its own, but rather that it at best flanked a whole slew of other authors doing remarkably dissimilare things. Nobody confuses Peake with C.S. Lewis, for instance, and neither of those are conflated with Tolkien.
Plus, the amount of criticial cred that SF&F generally got didn't really start reaching anything like mainstream acceptability until the mid-Seventies at earliest. I suspect, ironically enough, the one thing that allowed it to start getting exactly that was when the cultural products that took on those labels started making tons and tons of money, and could no longer be argued with as a cultural force. At that point, you don't have any choice but to start some kind of scholarly dialogue about such a thing.