Power Query - Custom Column - Less than Date

Ok, not technically Power BI (at this stage) as I need to do some data work in Excel before moving it into PowerBI but i'm trying to create a custom column in PowerQuery that has a formula along the lines of

if [company] = "CompanyA" and [date opened] < "01/01/2017" then "Pre 2017" else "2017"

But I am getting an error "We cannot apply operator < to types Text and Date" 

Appreciate this is probably really simple, and if in excel I could use DATE(), but I am new to PowerQuery and the syntax.

How do I get this to work correctly please?