College Arcanum 5E
Magic use in this world functions more like a mutant power or random gift from the gods. About 1 out of 100 people are born with some level of the Gift, although only about 1 in 500 have enough of the gift to be trained as a full Mage.
4 out of 5 Gifted have a minor gift that will never develop into true magic-use. Most of these people are left alone by the College and never manifest anything at all. A few manifest minor wild talents without training, but these are uncontrolled and rarely amount to anything more than being slightly luckier than most or having a “way” with horses, etc. These talents are not reflected in specific game mechanics. However, there are Orders that actively recruit people with minor gifts, because with training and dedication, they can learn to manifest some specific magical effects. These abilities are reflected in Specializations like Ranger, Templar, or Paladin.
Distribution of the Gift-
The Gift is not impacted by genetics. The child of two Mages has no more chance of having the gift than anyone else. It does not follow bloodlines, or wealth, or nobility. The lowest beggar child to the highest noble can have the Gift. This actually tends to support the theory that the Gift comes from the gods, a belief that many people hold.
Magic and Religion-
The gods do not grant magic to their followers like in most fantasy settings, although there are some who believe all the “gifted” are messengers of the gods, and plenty of people who are “gifted” with magic find religion and work for various churches. However, ultimately, there is no distinction between arcane and divine magic in this world, and just being a follower of a particular religion does not mean you can do magic- you still have to be born with the “gift”.