The division of Earth's time periods into distinct ages such as the Age of Aquarius stems from the Precession of the equinoxes.

But there are no sharp lines in the sky that mark clear boundaries between those zodiac areas, so the postulated change-over dates vary greatly.

However, there are some researchers who connect Earth's history (especially mythological and religious) with these Ages.

• The Age of Taurus (~ 4000 BC - 2000 BC): As Moses descended from the mountain with the 10 commandments, he was quite pissed to see his people dancing around a golden bull calf. So, symbolically speaking, he ended this age and a new one started.

• The Age of Aries (~ 2000 BC - 1 AD): The jews blowing the Ram's horn might stem from this age.

• The Age of Pisces (~ 1 AD - 2000 AD): Jesus is also known as the fisherman, and the Jesus fish is omnipresent. Jesus also said in Mat 28:16-20: "And behold, I am with you always, until the end of the age." That's not forever, and then it seems we should look out for the water man (Aquarius?) in Luke 22:10: "As you enter the city, a man carrying a jar of water will meet you. Follow him to the house that he enters" (house == astrological house?).

• The Age of Aquarius (~ 2000 AD - ...): Sooo, our next spiritual leader will have something to do with an Aquarius I guess. We'll be curious what he will have in store for us. Maybe he will even be on time in 2012... :->

In the process of piling this answer together, I actually found that there is a Wikipedia article on that subject with all the hypotheses: Astrological Age.

We can only wonder if there is more to this than mere coincidence and selective interpretation. And if so, are those coincidences merely a subconscious process on the collective human psyche?

Or is that whole game crafted by secret rulers behind the curtains? If so, what is their motivation? Maybe the Powers That Be use such ages as a map for orientation through these long periods of time in order to serve whatever agenda, or they are just plain bored and don't know what else to do with their (and our) time. :->

Wikipedia is not much help here. The article there claims that the period of time in which the Age of Aquarius resides depends on who you talk to, and the article itself contains a banner that says the sources within the article are all primary sources (i.e. uncorroborated).

In the 'Book of World Horoscopes' Nicholas Campion mentions at least seventy dates for the beginning of the Age of Aquarius covering a range of 1500 years.

The year 2012 is associated with the end-date of a 5,125-year-long cycle in the Mayan Long Count calendar, so it doesn't appear to have anything to do with the Age of Aquarius, or any other astrological phenomena.