It's as simple as subtraction...
Enter the formula
in the cell on page (sheet) 5 - or anywhere.
It's not clear from your question whether you want the difference between the first and last dates or between the first date and the present time. If you want the difference between a date and the time now, enter
To show the number of days difference, be sure the cell with the formula is formatted as a number and not a date.
In your example, from the first date (1) to the last date (4) is actually a difference of 3 days, not 4. If you want to include the first date as a day that has passed, then use
Minus one at the end causes the earlier date to count as elapsed by making it one day earlier.
Edit - Page Names:
In your question, you refer to "Page 1". In the formulas I cite, "Sheet1" is the name of the first "page" or worksheet in the file. Sheet 1, Sheet 2, etc. is the default name in Excel. If yours are actually named "Page1" then you need to use that name in the formula.
Edit - Starter Edition:
Turns out the original poster is using Excel Starter Edition and getting the error message "Excel Starter does not support external data connections". So - can't reference across pages with Starter edition.