It's interesting to note that Capricorn and Sagittarius are the only signs that are represented by beings that are part one thing and part something else. Gemini has the twins, but those are two humans. Scorpio has the scorpion and the eagle, but not a creature made of both. I hypothesise that Capricorn is the "first sign" in terms of describing the evolution of souls in the Earth. We began as Capricorn, the near senseless conglomeration of parts. From there, we progressed into Sagittarius, which is part horse, but with the torso and head of a man, symbolising (much like the Sphinx) man's dominion over his own animal nature.
It's also interesting to (once again) note the strange distribution of the traditional rulerships. They are placed in order of increasing distance from the Sun. The luminaries begin at the Cancer/Leo cusp and the planets are listed in proper, heliocentric order in both directions around the circle. If we stop at Saturn, we stop at the Capricorn/Aquarius cusp. If we include outer planets, the Capricorn/Aquarius cusp is where the lists from each side overlap. This also suggests that Capricorn may be the original "first sign," meaning that we would transition to the next iteration of the circle at the end of Aquarius.
If we assume that the birth of Jesus marked the exact beginning of Pisces, then we should reach the age of Capricorn around the year 4295 at our current rate of precession. If we make that assumption, that also means that we won't actually reach the age of Aquarius until around the year 2148. If we assume that the year 2000 marks the exact beginning of Aquarius, then we should hit Capricorn around the year 4148. Star-based astrology should hold the answer to exactly when we are now.