What type of variable should be declared to store a list of names and age pairs efficiently?

A dictionary is the ideal choice to store a list of names and age pairs efficiently. This data structure allows you to associate keys with values, making it perfect for scenarios where you want to map unique identifiers to specific data, such as a person's name to their age.

In this case, names can be used as the keys, while ages can be the corresponding values. This not only provides a clear and organized way to access each person's age using their name but also ensures quick look-up times for finding the age associated with a specific name.

Using a list on its own would require additional handling to keep track of the associations between names and ages, which could lead to inefficiencies and complications, as you'd have to rely on indexing and the order of the elements to manage pairs. An array has similar limitations, as it is typically used for storing homogeneous data and also requires additional handling for pairing. A string is unsuitable altogether since it is meant for storing text rather than key-value pairs, and does not support this kind of data relationship or retrieval.

Choosing a dictionary enhances clarity, organization, and efficiency when working with pairs of names and ages in programming.