Date variable to filter result for all previous years
There are many ways to get the beginning of this year, I think the most intuitive is DATEFROMPARTS():

DECLARE @BeginningOfThisYear date = DATEFROMPARTS(YEAR(SYSUTCDATETIME()),1,1);

SELECT ... FROM dbo.Customers AS c
WHERE NOT EXISTS 
(
  SELECT 1 FROM dbo.Orders 
    WHERE CustomerID = c.CustomerID
    AND OrderDate &gt;= @BeginningOfThisYear
);


Less intuitive ways include:

DECLARE @BeginningOfThisYear date = DATEADD(DAY, 
  1-DATEPART(DAYOFYEAR, SYSUTCDATETIME()), 
  SYSUTCDATETIME()
);


And downright terrible ways include:

DECLARE @BeginningOfThisYear date = CONVERT(date,
  CONCAT(YEAR(SYSUTCDATETIME()),'0101'));