OP can as well use
To get the formula to work for other columns it's enough to drag the formula right (right.clickinf on right lower corner of cell so that a cross is shown there, and then dragging ro right holding mouse tab down. And after that clearing the formula from abundant cells.

Didn't understand a thing about column A having a word in it? Do you mean column header? Or do dates in column A have some text before or after date? Or is in some cells a text instead of date?

And generally it is bad practice to have any summaries at bottom of data! You may have a situation where you must edit formulas whenever you add new row of data into table. Much better is have for any totals rows reserved at top of table. Additional bonus will be to use Freeze Panes feature to be Totals always displayed.