Take this quick unscientific test to determine how healthy your ears still are.
While human ears can ideally hear sounds from a frequency range of 8kHz - 22kHz, the hearing ability starts deteriorating post early adulthood, and it is common for people past 25 to not hear anything over 15kHz. Other than age, listening to high volume music or even iPod usage for extended periods are some common culprits for bad hearing.
So here is a list of MP3 sounds that go from 8kHz to 22KHz, to help you find out where your high frequency hearing cuts off. If you can hear the 15kHz sound and above, your ears are as healthy as a teenager.