In terms of firearm requirements, what must the board establish by rule?

The correct answer focuses on the establishment of additional qualifications for individuals carrying firearms. This is essential because training, competency, and adherence to safety protocols are paramount when it comes to security officers handling firearms. The board's role in setting these qualifications ensures that only individuals who meet specific standards in training and responsibility are permitted to carry firearms while on duty.

Establishing these qualifications helps maintain a high level of professionalism in the security industry and is crucial for the safety of both the security personnel and the public. Ensuring that security officers have the necessary training and qualifications aids in preventing incidents that could arise from improper handling of firearms.

The other options, while they touch on important aspects of firearm regulation, do not directly address the core responsibility of the board regarding the qualifications of those who will be armed. For example, setting a maximum age limit or specifying the types of firearms and ammunition may be relevant, but they fall short of focusing on the comprehensive training and qualifications needed to ensure competent firearm use.