I am not sure why people didn't like the function because It works for me. I created yet another sample table as shown below and the result using this query was fantastic:
USE testDB
GO
SELECT [ID]
      ,[FirstName]
      ,[LastName]
      ,[BirthDate]
      ,FORMAT (getdate(), 'yyyy-MM-dd') as Today
      ,dbo.fn_DateDiffParts([BirthDate]) AS [CurrentAge]
      ,[Hiredate]
      ,dbo.fn_DateDiffParts([HireDate]) AS [Experience]
      ,[Department]
      ,[Salary]
  FROM [testDB].[dbo].[Employees]
Output: