Wrong expression type error

[#1]

Hey Community,

 I have a formula that works perfectly when I use in a table column but will not work at all in my script. I'm certain I've overlooked something stupid but can't seem to figure it out. Anyone want to give it fresh eyes? 

dt3 << New Column( "Age Group", Character, "Nominal");

dt3:Age Group << Set Each Value(

If(

:Overdue Age < 1, Empty(),

1 <= :Overdue Age < 90, "<3 mo",

90 <= :Overdue Age < 181, "3-6 mo",

180 <= :Overdue Age < 366, "6-12 mo",

:Overdue Age > 365, "More than 12 mo"

));

This is the error I'm getting, below.

Thanks!