Hey, sorry for not noticing that shout sooner. My comment is mostly inferred, but some great event separated the Age of Legends from the age prior. (I refer to it as the Age of Myth because of the catechism at the beginning of each of the books "Memory to legend, legend to myth.") As for why I believe channeling was discovered at the end of the Age of Myth, it seems to be the defining feature of the Age of Legends, and the sudden prevalence of magic in the world would, in my mind, be sufficient in "breaking the world." Not literally, but figuratively, as I also believe Rand's breaking will be. Again, it's only an inference, and my own opinions coloring that inference, but that is why I made those remarks.