How to can hear dog whistles?

My mom has this dog whistle app on her iPhone and she was playing it for some reason and I could hear it loud and clear. At first, I didn't know it was an app, I thought it was the cord glitching out or something. She changed the pitch and I could hear all the dog whistles loud and clear, while she couldnt hear them at all. It sounded like someone was blowing a normal whistle right by my ear, thats how well I could hear it. Is that normal? I'm 18, if that counts for anything.

Yes, its normal.

The range of frequencies the human ear can detect gets narrower as you get older.

There are various products that exploit this fact, for example mobile ring tones that kids can hear but adults can't, or "crickets" that play noises to discourage teenagers from hanging around outside off licenses without disturbing genuine customers.

The more your ear gets damaged the less frequencies you can hear. Dog whistles are at an extremely high frequency, though I bet a phone is much lower than REAL dog whistles.

So your ear is better than most peoples, but not superhuman. Try it with a real dog whistle sometime.