It depends - some people are born with charisma, some learn it

Charisma, like anything else, can be bolstered by a genetic predisposition to having it. But that doesn't mean that it can't be learned. Even those who are naturals with charisma learn to use it better as they go through life, and those who aren't can still develop those skills anyway. So, determining a person's charisma depends on both nature and nurture.