My ears are 18
It's pretty horrible, actually. As I described it to Mom, "imagine someone playing a kicky rhythm on the blackboard with their nails." Actually, if anyone remembers the high-pitched squeal made by a roomful of Apple II-es, it's much like that -- and that noise used to drive me out of the computer lab. Which raises some questions. The NYT article claims that presbycusis, the natural aging-related hearing loss that makes adults immune to "Mosquito," starts in "early middle age." In other words, I should be able to hear this awful thing. So why was it ever economically feasible to blast it from speakers outside stores? Sure, you'd do away with teenage loiterers, but is that really worth losing all of your customers under 40? It's not the brightest of choices for a teen-only ringtone, either. I had a lot of middle-aged teachers, but a fair number of young ones, too... and if your teacher can hear your ringtone AND finds it exceedingly unpleasant, you are not exactly ahead of the game.
In any case, while I was sad to lose my story of psychological warfare, the technological ingenuity is actually quite admirable. It's a nice example of turning a weakness into a strength; if someone is going to exploit your ability to hear high-pitched noises, use high-pitched noises to keep your activities secret. And it indicates that the real difference between kids and adults isn't presbycusis -- it's techie know-how.