Which of the following is NOT a requirement for obtaining a security license in Texas?

In Texas, one of the requirements for obtaining a security license is that the individual must be at least 18 years old. This age requirement is in place to ensure that applicants are of legal age to hold a position of responsibility, which often involves public safety and the protection of property.

The other factors listed, such as having a high school diploma, passing a background check, and being a U.S. citizen, are not universally required for all types of security licenses. For example, while having a high school diploma or GED can be beneficial, it is not a stringent requirement for every position in the security field. Additionally, while some employers may prefer or require citizenship, the Texas security license does not mandate it as an absolute criterion.

Therefore, the option stating that one must be a U.S. citizen is not a requirement for obtaining a security license in Texas, making it the correct choice in this context.