I have 2 nieces - 16 and 13. The 16 year old (definitely NOT the NF) has always gotten straight As in school, is breezing through just about every AP class her school offers, plays sports, has tons of friends, and comes across as a very well-adjusted teenager. She has a self-proclaimed hatred of emotional or intellectual "depth" and could care less about art or poetry. Things come very easily to her and she rarely stresses about the future. She is a definite ESxP, with a very borderline T/F - she's bubbly and excitable, but also quite directive.
It's the younger niece that has me more perplexed. She's very sensitive, and even at a very young age, she wanted to volunteer in soup kitchens, etc... But in some ways, she's completely insensitive - making inappropriate jokes at awkward times and the like. Her mother claims she's just trying to improve the spirits of people around her, but I don't know... it seems off sometimes. That description could fit ENFP, which I've considered for her, but there's something very introverted about her. She's definitely a talker, has a lot of friends, and acts kind of bubbly and even scatterbrained at times, but it all seems like an act.
Unlike her older sister, she doesn't have the need to always be on the go and seems to enjoy being alone quite a bit. I also get the feeling that there's a lot of underlying depression or anxiety, although it's never verbalized. She's never really had an interest in an activity that has lasted long, although she does seem to like theater quite a bit. I guess she could be an INFP, but I'm thrown by the fact that she always seems like she's playing a role - so much so that I don't always know what to believe about her.
So, NFs... think back to your teenage years... any guesses or telltale signs I could look for?