To give more examples:

Red Mage would need maybe THM at 50 and GLA at 30. Dark Knight would be LNC or MRD at 50 and THM at 30.
Ninja would be PUG at 50 and GLA at 30. BLack Mage would be THM at 50 and maybe CONJ at 30, WHM is CONJ at 30 and THM at 30.

Etc! Use your imagination! At the end of these requirements, advanced jobs will be unlocked at 50, but you can rank them up to 75 to learn the class and its specific abilities