Here they are:
along the Ecliptic
|Duration in Years||Start Year||Shifted Start Year|
|Leo||35° 30'||2556||10880 BC||10458 BC|
|Cancer||20° 30'||1476||8324 BC||7902 BC|
|Gemini||28°||2016||6848 BC||6426 BC|
|Taurus||36° 30'||2628||4832 BC||4410 BC|
|Aries||24° 45'||1782||2204 BC||1782 BC|
|Pisces||37° 15'||2682||422 BC||0|
|Aquarius||24° 30'||1764||2260 AD||2682 AD|
|Capricornus||27° 45'||1998||4024 AD||4446 AD|
|Sagittarius||33° 15'||2394||6022 AD||6444 AD|
|Ophiuchus||18° 30'||1332||8416 AD||8838 AD|
|Scorpius||6° 30'||468||9748 AD||10170 AD|
|Libra||23° 20'||1680||10216 AD||10638 AD|
|Virgo||43° 40'||3144||11896 AD||12318 AD|
I've arranged this table so that the Age of Leo appears first in the list, which corresponds to the right starting point for this Great Year (10880 BC) if we accept that the turning point of Betelgeuse in Orion marks the midpoint.
But I've also shifted forward by 422 years the start year, because my initial choice of Betelgeuse is arbitrary and there are what I feel are strong mythological clues to the Aries/Pisces boundary being tightly associated with Year 0 of the modern western calendar.
The shifting has the effect of moving the Great Year's midpoint forward 422 years as well of course, from 2080 AD to 2582 AD. That would mean the Great Year midpoint marker would not be Betelgeuse but would instead be a line almost exactly straight down the middle of Orion less than half a degree west of Mintaka - which is rather more pleasingly symmetrical.
Naturally, these precise dates are somewhat misleading - the counstellation boundaries I've used are our modern astronomical ones and I believe the ancient astronomers themselves would not have tried to impose a purely mathematical tyranny of precision on precession.
Instead I suspect they would, by watching the sky, anticipate a forthcoming change of the vernal equinox position of the Sun from one sign to the next and begin predicting and watching for exceptional astronomical events (eg sufficiently notable conjunctions) that they would use to signify the moment of change from one World Age to the next.
However flawed my approach, at least I now have a better idea of how the Great Year might have been split up into Astrological Ages based on direct observation, prediction and ritual rather than simply dividing 25920 by 12. It's interested to notice that Scorpius's angular size on the Ecliptic is tiny compared to the other signs. 13th sign Ophiuchus - often described as just encroaching into the Zodiacal band - is much more signficant and yet...
PostScript I keep coming back to the story of Moses telling the Israelites off for worshipping a golden calf (Taurus symbolism) when he's just returned from confirming that the Age of Aries (lamb symbolism) has begun. On my crude figures that should have happened in 1782 BC, putting the biblical exodus back by about 400 years from the conventional dating (though not, it seems, too far from the date of the Hyksos Kings in Egypt).