Hmm, that's odd, it's always been available for me (but then I started ARR in Gridania back in the Beta and naturally only arrived in Limsa via the airship as part of the story anyway). I wonder though if map completion has anything to do with it (like not being able to teleport to an aetheryte you haven't yet attuned to). Still seems odd that Limsa's ferries would be locked til level 15 yet the ferries in Gridania are available from level 1. That's the thalassocracy for you I guess...