17 years old and can't hear above 15kHZ?

I came across this video today and surprisingly couldn't hear anything past 15kHZ

My hearing never concerned me at all and I'm not usually exposed to loud noises nor do I listen to very loud music - usually I set the volume halfway on my iphone

Apparently this is very bad, why is this happening.

I have exactly the same thing but I noticed it last year, when I was 14, and I'm not dead yet so I guess it's all good! Interested in whatever answers you get though.

Maybe your speaker/headphone can't make the sound. I can't hear it either even though i have a very good headphone… I don't trust the vid.

Most people can't, this is completely normal.

This is not really bad hearing, but some people with acute hearing can hear 20 KHZ.
I never could hear above 15-16 KHZ either, but can hear 12 HZ.
The device you were watching the youtube link on may not be able to pass frequencies above 15 KHZ, so this is a poor gauge for determining your audio range.
You could always consult an audiologist and have your hearing checked on valid equipment to be certain.
Here are plenty of charts showing human audio spectrum and hearing