When do I get to use my CE mounts?

[Kaitlen]

I have the mounts from the CE edition, but I'm not authorized to use them...somehow. I know there's a mission from the Grand Company to earn a chocobo (don't know when that arrives), but I can't use any mounts until that point?

Yep. You need to complete the Company Chocobo quest before you can use any mount.

Join a Grand Company > Start the Chocobo Quest (My Little Choco) > Get 2,000* Company Seals > Get Chocobo and mount access.]

I thought it was 2,000 Seals, but maybe it's changed to 1,000 now to get the Issuance Certificate from the company quartermaster.

Edit: For Main Story Line > You need to be at Level 20 "Hero in the Making" (Completed). This is the access point to get the above quest.