date update in Pages 5.6

Not directly. But it can be done with a one-cell table, where you double-click on the cell, and then enter =now with a return. That will fill the cell with the current, default date string. You can alter that in the Cell tab's Data Format Date and Time settings.

Then, you hide the table boundary via Table panel : Table Outline : None. You may need to change the Arrange tab settings for Object Placement and Text Wrap to move the one-cell table where you want it in the document.

You could move that datestamp table cell over one of the header or footer sections of the document, and then from Arrange menu : Section Masters : Move Object to Section Master. Then that date information would be populated on very page of the document in that location.

To avoid fiddling with this in the future, you could save it in a new template.