Steam: Sorry, but you're not permitted to view these materials at this time

So there I am... launch the STEAM application, click on Fallout 3 to get an addon for it and ...

"Verify your date of birth"

And I accidentally click "OK" before I really read the screen and now it thinks I'm born TODAY so it says "Sorry, but you're not permitted to view these materials at this time"

Tracking down how to kill that setting was a pain in the ass.

So here it is, everyone:

Delete the contents of the "cache" folder in the steam install location and restart Steam (make sure to exit the system tray Steam application first too.)