Automated Checkbox not working

[4Justme2]

I have a script to determine whether or not a person is a teen at the time of a specific event:

teenAtTheTime, calculation, numeric result

Case ( ageAtTheTime>12.99 and ( ageAtTheTime ) <20 ; "1"; "0" )

I placed the field on my layout page and formatted the field as a check box, boolean = 1

How do I get the checkbox to be checked automatically if the condition is true? The way I currently have this set up nothing is checked when the condition is true.

[No_access]

I tried what you have and it seems to work perfectly for me.

I created 2 fields. teenatthetime with your calculation and is a checkbox with the only value in the value list being 1

and ageatthetime number field so I can enter the age.