Their talent is based on two components: Magic and Mana.
The talent for magic is apparently hereditary with only one descendant per generation inheriting the family magic . However, Mima claims to be able to bestow magic to another human . It is not known if there really are means for humans to obtain magic other than via inheritance.
Every human has an inherent amount of mana. Without mana it is impossible to use magic. Thus, magicians are usually humans with a high amount of mana.
The Perfect Magician
Mima calls himself the Perfect Magician, a claim supported by Sage Labin . Besides promising the princess to be able to 'give' her magic and defeating a fairy with ease, he constantly uses his magic to float around, change clothes and even teleport.
As of yet no other magicians were seen performing magic, but his skills seem unusual judging by the reactions of Prishtina who knows several other magicians.