Many creatures in Gaia have magic but there are limits based on species or inherit abilities.  Such as a forest nymph. They can make things grow and can to extent control the plants but this magic can't extend to water for example, or fire. Mages are born with innate magic but they are born into a 'sect' of magic, meaning it is much easier to learn from that 'sect' and almost impossible to branch out. 

    Certain humans can use magic. Usually its genetic but a human that can use magic(called casters) can show up in family that don't have history and families with a history can have a normal human member. These casters, have a different set of rules. For humans, magic has a price. Energy. The casters own life force.  Casters are born with something called a core, hidden behind the heart. This core allows casters to convert their own energy into magic. Not all Casters chose,however, chose to go beyond the magic spells or don't chose to learn magic at all. It can kill the caster or burn away their magic permanently, depending on what is trying to be accomplished. This is why young and inexperienced castors must be careful. Magic is like a muscle and must be built up over time. The body must become used to its life force being used this way and must learn to compensate.