In Australia, size 9 could be quite large. There are two systems of sizing for adults. Size 9 in the one that is used for mens' shoes and sports shoes would be sort of average for a man but quite large for a woman, but in fractional fittings, which have half sizes and different widths, size 9 would still be slightly larger than average for a woman, but not much. I am size 8 in that system, and 5-6 in sneakers, and I am about average.

Of course, this wasn't an Australian song, but maybe some other countries have the same system?

Jenny