I couldn't immediately relate a 600 year span to anything in astrology, but a little research soon brought up the following at sacred texts.com:
The “arc” of capitalism, according to this school, is about 600 years long, from 1500 to 2100. It is our particular (mis)fortune to be living through the beginning of the end, the disintegration of capitalism as a world system. It was mostly commercial capital in the sixteenth century, evolving into industrial capital in the eighteenth and nineteenth centuries, and then moving on to financial capital—money created by money itself, and by speculation in currency—in the twentieth and twenty-first. In dialectical fashion, it will be the very success of the system that eventually does it in.
The last time a change of this magnitude occurred was during the fourteenth and fifteenth centuries, during which time the medieval world began to come apart and be replaced by the modern one. In his classic study of the period, The Waning of the Middle Ages, the Dutch historian Johan Huizinga depicted the time as one of depression and cultural exhaustion—like our own age, not much fun to live through. One reason for this is that the world is literally perched over an abyss. What lies ahead is largely unknown, and to have to hover over an abyss for a long time is, to put it colloquially, a bit of a drag. The same thing was true at the time of the collapse of the Roman Empire as well, on the ruins of which the feudal system slowly arose.