Final answer:
The specific percentage of people in the United States with at least one major risk factor for coronary heart disease by age 20 is not provided in the given references. However, age, gender, genetics, smoking, diabetes, obesity, and physical inactivity are all risk factors for developing cardiovascular diseases.
Step-by-step explanation:
According to the Centers for Disease Control and Prevention (CDC), the prevalence of major risk factors for coronary heart disease in the United States is influenced by various factors. However, it is important to note that the specific percentage of people with at least one major risk factor for coronary heart disease by age 20 is not provided in the given references. The age of a person is a significant risk factor for developing cardiovascular diseases, with a tripling of cardiovascular disease risk with each passing decade of life. Other risk factors include gender, genetics, smoking, diabetes, obesity, and physical inactivity.