The Conventional Span and Jung's Aion

On the standard even division of the Great Year, the Age of Pisces is generally placed beginning around the turn of the era and running, depending on the writer, into the twentieth, twenty first or as late as the twenty seventh century CE, following the Age of Aries and preceding the Age of Aquarius. Its most influential treatment is Carl Jung's 1951 study Aion, which reads the fish as a recurring symbol across the roughly two millennia associated with the age, from its use as a covert identifying mark among early Christians to its appearance as an astrological glyph, and treats the shift toward the following age as a psychological as well as an astronomical transition, part of Jung's broader argument about the changing symbolic contents of the Western collective unconscious.

Jung's study is explicit that it uses the astrological ages framework as a structuring device for psychological and symbolic material rather than as an astronomical claim he was independently verifying, and later commentators have generally read Aion the same way: as an influential work of analytical psychology that borrowed the Age of Pisces concept, not as an authority on when the age itself began or will end.