Magic is normally not something trivial to control. In most stories, it can take years of practice to get just the basics, and in some cases the only ones considered masters are ones with decades of experience.
So, your specific magic system is one that is moderately complex, something that is not intuitive for normal humans. Some humans however, do find it fairly easy to understand. Their genetics mutated how they think ever so slightly so that they can figure it out easier. There are numerous examples of real life people who can think in ways other humans find unimaginable. If one of these people had a child, that child is likely to have a similar mind, and similarly have a talent for understanding how to use magic.
That is not the only way to get really good at something though. Mastery as a child frequently will carry on through adulthood. Speaking, and writing are primary examples of such things. 917
We learn these basic functions as a child, and then as adults, they are trivial to us. Children's brains are built for learning and understanding new things, So a child growing up in a magic rich environment would likely have their brain molded by that magic. They too learn about magic intricately without even knowing its magic, and being children will try and discover what it is. This will lead to these children naturally discovering magic, giving them a base knowledge and understanding far beyond what any adult could ever learn, because they were literally raised by it.
Both systems are fundamentally different. While both will find it easier to grow, those raised by magic will start off at a higher level, and will more easily learn the basics/intermediates, but later on the Genetics will likely catch up and surpass them. Raised by magic individuals will also likely find it far easier to manipulate their magic, conserve stamina/magic power, and otherwise have more fine control of it. They would be more <PERSON> of all trades kind of users. Genetic individuals on the other hand would be better One trick pony kind of magic users, Mastering only a few things, but they would be more creative in their useage, as well as better strategists.
Of course, Those ideas are not set in stone, and certainly can be mixed and matched based on the individual. 227