My guess is that this service is not actually supposed to be used by teenagers, thus there aren't a lot of them around. From italki's terms of service:
The Site, Application and Services are intended solely for persons who are 18 or older. Any access to or use of the Site, Application or Services by anyone under 18 is expressly prohibited. By accessing or using the Site, Application or Services you represent and warrant that you are 18 or older.
There are a few reasons why it's hard for you to find English speaking teenagers from the US, UK, Canada, or Australia.
1.) Most teens are too busy / don't see the necessity of speaking another language yet. In America, we are required to take a language course in high school, but is a chore at that age. Most students would see any language learning as boring.
2.) You're not offering Japanese, Spanish, or Korean. It is the 3 most popular languages in America right now; Japanese because of anime, Korea because of the k-pop wave, Spanish because many people in America speak it. Unfortunately, it leaves other people who do not speak these three partner-less.
I hope that you'll be able to find a language partner your age soon enough! ❤️
Well, there can be a lot of reasons actually. Sometimes teenagers are busier than adults. In my experience, my students who are teenagers have a lot of homework and extracurricular activities and so most of them have very little time to study.
Another reason is the lack of initiative to learn. Most are actually forced by their parents to learn.
Trying to improve my English...
I'm from Brazil
If you want to talk, just sand me a message