You can use the airship to go from Gridania to Limsa Lominsa. It's the staircase down in the adventure guild in Gridania. If you are a grand company member you can buy a chocobo for 3k seals. If you are not a member you can rent a chocobo, but it's time limited.
And you can get with level 30 a gobbue mount for free until 2.0