the coordinate you want to set must exist
I was avoiding that!
Maybe you don't need TMemo. It's an oriented-line control like any Edition control. Even TSynEdit works that way.
If you want to locate text in any arbitrary position you can use a char matrix like a Terminal screen or DOS screen. I have simulated a Terminal screens using TSynEdit but it need to be carefully programated.
A Stringgrid must do the trick but it's a table control and behave like that.
Other option is to draw directly the text in the Canvas or using some graphic library. If you need to edit the text it's more complicated. You could manage dynamically TEdit controls.