Imagine the Tropical zodiac with its 12 equal, constructed Signs rotating through the Sidereal zodiac with its 12--two spoked wheels, one turning within the other. Now use the First Point of Tropical Aries as the Age-indicator for the Sidereal zodiac. Each time the spokes of the Tropical wheel line up (coincide) with those of the Sidereal wheel, the First Point of Tropical Aries begins moving through a Sidereal sign, and that sign's Age begins. The location of the First Point of Tropical Aries is measured to the nearest second of arc--we know exactly where it is. What we can't agree on is exactly how to locate the spokes of the Sidereal wheel. And, due to the extremely slow movement of the First Point of Tropical Aries, even a small difference in where the Sidereal signs are placed on the Zodiacal constellations results in a large difference in when an Age begins. So, it's just a matter of opinion on how to locate 12 equal signs on the 12 unequal constellations that
causes the disagreement.