The "Golden Age" in science fiction is often restricted to 1936-45, and is strongly associated with John W. Campbell's Astounding magazine. On this web site, I use the phrase to refer to roughly 1930-1959 and the generation of writers in that era. After all, many of those authors wrote much of their best work through the 1950s: Childhood's End, Foundation Trilogy, Martian Chronicles, A Door Into Summer, Mission of Gravity - the list goes on and on.
So why should the "Golden Age" be considered ended with the end of World War II? There is also much debate about when the best sci-fi has been written. I think there's a good argument that the "Golden Age" of quality ran about 1970-1989, since many of these "dinosaurs" were still doing great work, while good newer writers had also come on the scene. It is probably true, though, that the term "Golden Age" has been used so long to refer to 1936-45 that it's historically set in concrete, so there's little point in arguing about it. But on this web site, at least, it's re-defined to 1930-1959.
One reason I am fond of the older stories is that, in general, there was more focus on the "hard" sciences like physics and astronomy, and more optimism about the future. Most recent SF has focused on such "soft" sciences as sociology, psychology, and politics, and has been much darker.
But I'm just speaking in generalities. There are some very good "hard" writers today, such as Stephen Baxter. Golden-Ager Ray Bradbury, hardly a raging optimist focused on physics, is one of my favorites. And variety makes the field richer.
Partly, too, I'm fighting the tendency of many people to pay attention only to what's new. And part of my motivation is nostalgia, I'm sure, since these writers were still the biggest when I began reading SF in the 1970s. But, whatever the complexity of the matter, I have a fondness for the earlier world of science fiction, so I'm doing my small part here to promote it, lest it be forgotten completely. Sorry there are few women featured on these pages, but there just weren't many in SF back then. OK, I've done my little harangue, so now begins my "Golden Age" section.