Which of the following is a requirement for serving documents in Arizona?

In Arizona, one of the primary requirements for serving documents is that process servers must be licensed. This licensing ensures that process servers are trained and knowledgeable about the laws and regulations governing the service of process, which is a critical function in the legal system. Obtaining a license typically involves meeting certain educational and experience criteria, which helps maintain a standard of professionalism and protects the rights of those involved in legal proceedings.

Licensing also serves to instill public trust, as individuals can be assured that the person delivering legal documents has been vetted and adheres to the legal requirements for proper service. This is particularly important in a legal context where the proper service of documents is essential to uphold due process rights.

The other options relate to requirements that may not specifically apply to all process servers in Arizona. For instance, being over 21 years old may be a guideline in some jurisdictions but is not a universal requirement. Additionally, a high school diploma is not explicitly stated as a legal requirement, nor is the necessity for legal representation to serve documents. Therefore, having a license is the key requirement that validates a process server's qualifications and capability to perform their duties effectively.