Let's say you have value (7, 3 ot whatever) in A1 then you can use the following formula in Conditional formatting:

=ROWS(G$10:G10)<=$A$1 if you want to start in G10.
In the field Applies to can you write for example =$G$10:$G$100 if your max value in A1 will be 90.

You can use the Format Painter to copy that conditional formatting to another start cell (ensure that the formula has same row number both before and after the colon). Then you can go to the field Applies to and set the reference to what you want.