What is the age requirement to apply for the N-400 application?

To apply for the N-400 application, which is the Application for Naturalization, the individual must be at least 18 years old. This age requirement is in place because the application is meant for adults who are seeking to obtain U.S. citizenship. The legal age to be recognized as an adult under U.S. immigration law is 18, which is why this age threshold is established.

Younger individuals, specifically those under 18, can be included in their parent's application if the parent is qualifying for naturalization, but they cannot independently file their own N-400 until they reach the age of 18. This ensures that all applicants are legally capable of understanding and fulfilling the responsibilities of citizenship. The other choices suggest age thresholds that do not align with the U.S. immigration requirements for the application process.