Here's a thought. Consider the venerable spreadsheet. No, not the program, but the piece of paper. It was a regular array of cells, with column and row check sums and corner balancing for verification. They were used to hold accounting data back in the days when this was done by hand.
While not data in memory, it does embody the concept of a regular array of data.
I can't find a date on the use of paper spreadsheets, but I did find this:
However, the spreadsheet has been in existence, as a paper based
product, for longer than any of the computer based products. In the UK
it was called “Multi-column analysis paper”. In the USA it was called
a “spreadsheet” hence the name of the computer based version.