cell phones can tell you if you're old

I feel old all of a sudden. No, not because my 24th birthday is approaching, it's because of a story on Canada AM.
The story was about a cell phone ring tone that adults can't hear. The frequency is too high for adults, but youth can hear it. The idea is as we grow older we lose the ability to hear certain frequencies.
They played a clip of the ring tone...and hope as I might, I couldn't hear it.
The ring tone has two purposes: 1. to be able to play jokes in teachers in school...where the phone is ringing and the whole class can hear it but the teacher doesn't realize anything is happening...not a very funny prank but I guess it's entertaining for the class...and 2. to allow them to txt each other in class where it's not allowed...though I don't know why they don't just turn the cell to silent mode?
But the bottom line is I can't hear it.
It's official, I'm old.