There are different kinds of eras one of which is related to a specific period in a worldly observed activity.
An epoch is a division of time into a non-constant number of years. The Middle Ages and the Bronze Age are examples of eras. (source: Wikipedia)
The Age of Aquarius stems from the position of the sun, ancient astrology and observed activity in the universe.
The Age of Aquarius is related to the position of the sun in our solar system and beyond. (source: fingerprints of the Gods Graham Hancock) A perpetual movement of stars, suns, planets and our moon give their light from a different angle. Because this happens, we get other impulses through our sun. The impulses coming to Earth at this time are related to the prevailing constellation rising behind the sun. And now that’s Aquarius, that was the Pisces sign. These are periods of more than 2000 years. The transition period that we have now gone through from the Age of Pisces to the Age of Aquarius has taken about 80 to 90 years.