I am currently a volunteer examiner on this side of the United States. In February, a father and son came in; the son was just 7 years old. They both took the Technician exam (similar to China's A-level), and then in April, they both took the General exam (similar to China's B-level). The son passed, but his father only scored slightly below passing.
In amateur radio in the United States, it has been a popular hobby for older adults in recent years. Various organizations are trying to attract younger people to join. Typically, the test takers at this venue are mostly college students and high school students; however, seeing a 7-year-old child who is just starting elementary school is quite rare.