And what's the cut-off age--from a visible perspective--when it becomes rude for young children to ask this question? If that cashier appeared to be around 18, would the mother have corrected her child? What if the cashier looked 25? Suddenly, the question is rude? Why isn't it inappropriate when the cashier appears high school or college age?

I was a cashier when I was 16. I did as good a job as any 50-year-old cashier. Yet it would've been considered okay if a young child asked my age, but not the age of my 50-year-old coworker.

And what's the cut-off point where it's OKAY to ask someone's age? 18? 25?

I'd be curious to know what age that little boy appeared (3? 10?) and what age the cashier appeared (20s? 50s?)