You start it at level 30! no need to relevel all the way.
This is similar to how jobs are picked up later on - DRK, MCH, and AST start at 30 (require lvl 50 and entrance into Ishgard) RDM and SAM start at 50 (and require 60 i think) and DNC and GNB start at 60 (and require 70… i think)