Here is the formula's syntax. (BTW, don't go looking this up in the Help section as it is a "secret" formula.)
=DATEDIF(Earliest_Date, Latest_Date, UnitOfMeasure)
Here's how it works...
1st argument: A2 is the cell reference for the early date.If you prefer to calculate the WORKING days (excluding weekends and holidays) you can use the NETWORKDAYS formula.
2nd argument: For the late date, I used the TODAY() formula so it is dynamic for whenever I open the spreadsheet to have the current date.
3rd argument: The unit of measure can be either "Y" for years, "M" for months or "D" for days, depending on how you want the results to be calculated.
=NETWORKDAYS(start_date, end_date, holiday_range[optional])
Here it is in action...