I have a good friend who is INFJ, and I'm INFP. I would classify her, at times, to be "immature."
As INFP, I like to discuss different topics, potentially controversial ones. I don't neccessarily have a set opinion on the topic, but rather prefer to discuss so as to maybe better understand it, or come closer to finding a solution. I like to bounch ideas around, and get other peoples viewpoints.
My INFJ friend is much more conclusive, and has her opinions set in stone. When trying to discuss things with her, if I bring up any idea or statement that conflicts with her opinion, she shuts down, becomes very defensive, and will not discuss the topic any further. She will literally end the conversation with "well thats not what I think, and i don't want to talk about it anymore."
She is a very unique, smart, and gifted person, however, she has been unable to find any productive outlet for those strengths. Instead, she focuses most of her energy and identity on which boy she is dating. Having a boyfriend is the most imortant thing in her life, it gives her validation and a sense of worth. She is 24, and hasn't seemed to find anything else for herself that makes her happy, besides boyfriends and partying. and i don't want to even get started on the PDA she excercises, almost as if saying to the world " look at me, i'm pretty, i am loved, i have a good looking boyfriend, i am somebody."
She is usually very outwardly sweet, innocent, and kind. However, there is a darker side to her. She use to have a bit of a drinking problem, there were a few nights i witnessed her become extrememly drunk. when under the influence, horrible things tend to come out of her mouth, she turns nasty, crazy, almost posessed, its kindof scary. I think infj's hold back alot of themselves, and sometimes if under the influence, its like all the anger and resentments they have can come spilling out.
this is just my exerience, i don't know any other infjs besides her. when she is in a good state, she can be a wonderful friend, fun, good conversation. but when her negative quality's turn on, i sometimes cant stand being with her. im a loyal friend to her becuase i've known her since kindegarten, but sometimes it can be hard to be her friend.