According to the Compendium book, the ability to use magic is a genetic trait. That's why Espers can use it but people like Odin can't - Odin just doesn't have the genes for it. Dedicating studying is also needed, hence Esper Mansion being a magic school of sorts.
With that in mind, let's look at Zio. He uses magic, but there's no sign of anyone being on Motavia to teach it. Do you think Zio was born with magic ability and developed it, or did all of his power come from his association with Dark Force?