Why Can't I Trade Yellow Gathere's Scrips?

[tdb]

If I'm not mistaken and my memory doesn't betray me, those NPC will be unlocked when you hit your first 80 as Crafter/Gatherer. For now exchange what you have in Rhalgr's Reach.

I'm pretty sure I was able to trade with the Crystarium NPC before reaching Lv80. I had unlocked the Crystalline Mean quests though, so that's another thing that might act as a gate.