The example in cell A7 uses the YEAR function to extract the current year from the TODAY function in cell A2 and then subtracts from that 1999 to find the difference between the two years 2018 - 1999 19. In above formulas 2 indicates to add or subtract two weeks you can change it as you need. For the difference between A1 and Todays date you could enter.
For example you can format dates before today or format dates greater than today.
Or make a generic today minus N days formula based on a cell reference. If you change the number formatting of a cell that contains a date to General or Number you will see number between 1 and 40000. 60 days prior to today. TODAY 7 OR TODAY B13 Here either cell reference B13 or 7 is used along with today function.