How can the period immediately before Superman be a Dark Age, when it was literally just four years at most? I can see the idea that there was an extensive prototypical period of time where different kinds of comic books (books that reprinted the newspaper comics) were tried out, but once Max Gaines solved how to package comics for the mass market, lots of kids were buying them and the medium exploded with new titles.
Once that happened, there was a brief period (1934 - 1938), where Siegel and Shuster had already created Superman and were trying to sell him to the newspaper syndicates, which is how Max and Sheldon Mayer saw the strip and could remember it later. Mayer was already doing his Scribbly for POPULAR COMICS. Shuster and Siegel were already creating several different features for National Allied. Centaur had introduced the Clock. Will Eisner and Jerry Iger had created Sheena the Jungle Queen. If the market didn't exist for comics all in colour for a dime, with a mass of consumers buying them, no one would have noticed Superman when he arrived on the scene in ACTION COMICS.
It's kind of like arguing over what's more important, the point at which the Big Bang happened or the point immediately after the Big Bang where the universe was created. To me the creation of the modern American comic book and the creation of Superman are so closely linked that I favour the earlier date as that's what allows the individual characters to be created. And there were several original characters being created even before Superman. I like Superman, too, but I'm not willing to give him sole credit for the popularity of comics in the 1930s.
This site puts 1897-1938 as the Platinum Age.
But reading through it, I'd probably start at 1922 with Comics Monthly, the first monthly comic periodical.
"There's magic in the sound of analog audio." - CNET.
I'd put the start of the Dark Age in 1986 since Watchmen, Swamp Thing, and The Dark Knight Returns were all dark (but good) and set the tone for many imitators, most of which got the "dark" part but not the "good" part. The speculative boom, the overexposure of Wolverine-type killers, and the terrible art typifying early Image books were part of it as well. The light began to dawn again with works like Marvels and Kingdom Come that explicitly challenged the darkness, and Morrison's JLA and Busiek's Avengers and Astro City which emphasized heroism over angst.
I'm on the fence. I'm more inclined to think we had the Dark Age until 2010s (maybe the New 52 as turning point).
Since then, this Digital Age full of relaunches, diversity pushing, movies influence, constant changes of writers and status quo...