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.
Always deliver judgements from the Stars in general terms, or if thou dost otherwise let it be when thou hast very evident testimonies and in great and weighty matters. - Cardan Girolamo (1501-1576)