1. I'm in my early 20s.
2. I'm counting about 8 people, but mind you I am an introvert that doesn't usually try and get to know that many people. However, I found that those I recognize as NT usually stick out (especially the NTJs).
3. I would say it is probably correct. I have no reason to believe otherwise. I definitely don't think it is that common, but they are out there.