Problem with steam and age restricted content

[Mobsta]

I signed up to steam
All went well... browsed some games etc
Found COD - entered 1st Jan yesterdays date...
Was told "Sorry, you are now allowed to view this game at this time"
(self inflicted stupidity etc)

Googling tells me I need to close the program and open it again, for this message to go away.
Ive done that a few times, but still get the same error message.

How do I convince the system Im 18+

[Xerstead]

When you close it is it still running in the system tray? reboot?

[tenohfive]

Xerstead said:

When you close it is it still running in the system tray? reboot?

That should do it, I've done the same before.