"...it is important to note, that you are not necessarily one or the other. Most people have some of both extrovert and introvert in them..."

In a giant study from 2005, the highest scoring cultural groups for extraversion on average were Brazilians, French Swiss and the Maltese, while the lowest scoring were Nigerians, Moroccans and Indonesians.

The highest scoring for openness to experience were German-speaking Swiss, Danes and Germans, while the lowest scoring on average were Hong Kong Chinese, Northern Irish and Kuwaitis.

Percents

According to Science of People, personality is partially inheritable. They broke down some average numbers for how big a percentage of certain things is inherited:

Openness: 57%

Conscientiousness: 49%

Extraversion: 54%

Agreeableness: 42%

Neuroticism: 48%

*These are generalizations and can all be both significantly higher or lower

Inherited personality

Your "level" or introversion/extroversion is partially inheritable It can be fully inherited, not at all, or in between. According to Cain, "introversion is only 40-50% inheritable. This means that in a group of people, on average half of the variability in introversion-extroversion is caused by genetic factors" (Cain 108-109). This doesn't mean that everyone inherits 40-50 percent of their parents personalities, but more that it's an average. For some it might be close to 100%. For others, closer to 0%.