Form The CE info
Adventurers will be able to ride a variety of mounts for transportation in A Realm Reborn - including chocobos, Magitek armor and more! With this bonus, you'll be able to hop aboard a coeurl and chase down your foes!
* Players will be able to ride mounts once they have reached level 20 and have obtained a chocobo.
It would seem you need a chocobo form Grand company before you can use any mount. People using them now got Chocobo in 1.xx