People naturally create categories. Just like learning a native language happens naturally, so does learning to categorise the world around us. Categorising doesn’t emerge as a skill until about age 7. Younger than 7, and certainly younger than 5, thinking about categories just doesn’t make sense to children. After the age of 7, however, people become fascinated with categorising information.

https://www.blog.theteamw.com/2011/02/22/100-things-you-should-know-about-people-62-people-love-to-categorize/