There are many resources to help you identify and date a piece when you know the manufacturer.
My “go-to” reference materials for dating and identifying pieces for which I know the manufacturer are two much-used reference books: Smith & Wafford, The Book of Griswold & Wagner, Favorite, Wapak, Sidney Hollow Ware (5 ©2001 (commonly called the “Red Book”).
Gate marked pans typically do not have the manufacturer’s name on them.
Gate marked pans are the oldest of the old cast iron cookware; almost certainly antique.
If you click on “visit page,” it will link to the page where the pan is featured.
There, if you are lucky, you will find identifying information about your pan.
Absent markings on the pan, it is often impossible to identify the maker of a gate marked piece.