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.
The Moon answers those who are ruled by Venus, and Venus answers those ruled by the Moon. - Picatrix (Andalusia, ~1000.AD)