This would categorize as implicit atheists adults who have never heard of the concept of deities, adults who have not given the idea any real consideration, and agnostics who assert they do not believe in any deities (even if they claim not to be atheists).
This would categorize as implicit atheists adults. Implicit atheists adults are adults. These adults have not given the idea any real consideration. These adults have not given the idea agnostics (even if they claim not to be atheists). They do not believe in any deities. This is what these agnostics assert. These implicit atheists adults have never heard of the concept of deities.