Explanation:

- Social group: This term usually refers to a collection of people who interact with each other, share similar characteristics, and have a sense of unity. The age group by itself doesn't imply interaction or unity.

- Category: This is a group of people or things that share a common characteristic. Age group is a typical example of a category because it is a classification based on a shared attribute (age).

- Aggregate: This refers to a collection of individuals who are together in the same space but do not necessarily interact. It's more about a gathering rather than categorization.

- Collectivity: Similar to an aggregate, this term often denotes a group of individuals who share a common goal, but not necessarily a category based on age.

Correct Answer: Option 2 - Category