Julian descends from the Roman family name Julius, whose own origin is debated -- proposals range from "youthful" or "downy-bearded" to a link with Jupiter. What carries forward regardless of the exact root is an association with early promise, someone still arriving at their full shape rather than already fixed.
Saturn is under the Sun beams until he be 15 degrees distant from him. Understand the same of Jupiter. - William Lilly (1602.-1681.)