It isn't possible to tell the nationality 'when you were nine', because...
...there is no common national flag that contains a section featuring four quadrants of black, yellow, red, and white.
What?? Well, take a look at the other 9 listed above...
If we look at the national flags for these countries and then compare them with the International Maritime Signalling Flags for numbers we can see that the designs of each of the maritime flags can be seen (pretty much) somewhere within the designs of the national flag, with corresponding colours and shapes.
The design for a number 9 flag, though, involves four colours that don't commonly appear in national flags together, and particularly not in this desired orientation.
Although, saying that...
...with a little rotation, you might be a member of the Bandera Maya people!