Big

undefined:

Big refers to a headmate who behaves or feels like an adult. While the exact age of a big is often related to the age of the system' s body, it is generally at least 18 years old.

Related Terms
Big is often used in contrast with middle and little, which are other common age indicators.

Age Sliding is when a headmate varies in how old they feel, often going back and forth between adult and little, but can be any ages.