You're not senile. Here's what I figured out and it is a little convoluted:
These instructions assume you are starting on a screen where you are actually playing a level.
Click on the two vertical green lines in the lower left corner.
On the next screen, click the red X icon on the right.
On the next screen, click on the two vertical green lines in the lower left corner.
On the next screen, hit the globe icon in the lower right corner.
On the next screen, hit the vertical green lines in the lower left corner.
On the next screen, click on the red X.
On the next screen, click on the red X.
Basically you want to exit out to the map, and then you can proceed to close out the game from there.
I think if I was more familiar with the interface on handheld devices, the interface would be more intuitive. Maybe there's a shortcut way to exit, but I am not seeing it.