So the old saying goes. However, from what I've read over the past couple of years, the corn really needs to be more like waist-high by the 4th in order to bring in a good crop.
The 3-sisters corn I planted with my beans & squash is doing awesome. It's a dent (field) corn called "Oaxacan Green Dent". Some of the stalks are as tall as me.
The stalks completely tower over my oldest son!