Almost every source agrees that the Silver Age began with the publication of DC Comics' Showcase #4 (October 1956), which introduced the modern version of the Flash.
This age was also marked by the creation of the Comics Code Authority
that regulated the content in all the books, with the ones approved being stamped with CCA approval stamp on their covers.
Towards the end of the 1960s, the comic industry experienced low sales across the board. They were forced to re-invent themselves, and these efforts heralded the Bronze-Age. The following estimates of its duration have been found: