Auto fill to last row (number of rows will vary) - SOLVED

Hi all I've been using a macro to figure out the age (in days) of product on our shelves using excel.
I get a daily report on the items with the date they were booked in.
I have a macro set up where by it inserts a new column and subtracts the the cell in the corresponding row from today().
I currently have this set up to run all the way down to the 1000th row but would like to clean it up so that it runs to the end of the report based on the first column in the report.

My current macro:

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I have tried this solution based on one I found on here and replacing the last 5 lines in the above but it is returning a 1004 runtime error

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Any ideas what I'm doing wrong?

Thanks