Stop User From Publishing an Event if the Start Date is Before a Certain Month Using Rules
I'm not sure that Rules is required to do that.

I would rather use Field Validation module. It is able to configure complex validation rules for any field.

In its submodule called "Field validation extras" there's a validation rule that will help you, it's called "Date range2". You can set a specific minimum date according to your needs, and a far enough maximum date.