...has nothing to do with peoples' first names. Take a look at a globe or world map, and notice the lines of latitude a bit more than 23 degrees north and south of the equator. "Tropic of Cancer" and "Tropic of Capricorn" are what you'll almost certainly see. If you want to learn more about why those are anachronisms, search the Internet for "precession" and you'll probably find something among the first few hits that explains why. Hint: Unlike character names being off by decades or even centuries, the naming of the aforementioned parallels are outdated on the scale of millennia.
Just as the Mid-20th Century has become an "idyllic" period for childhood, the "astronomical idyllic" period is around the time of Christ and the century or two before. This also explains why the astrological "sun signs" largely do not match the actual constellations anymore.