I would like to begin by simply stating that I am new to these forums. So, hello!
I have taken the MBTI several times in the past year. I was initially typed as an INFP before retaking it to get INFJ. Both of the archetypes resonate with me, thus I label myself as an INFX. Furthermore, my Ni is just as strong as my Ne, and they are often interchangeable depending on what I feel like.
However, upon thoughtful consideration, I have recently begun to organize my life as an INFJ would. After all, I have now left the mess that is my parents house, both of whom are "P" types. I have also noticed that, by doing this, my Ni is becoming more dominant than my Ne; and it is truly empowering to be able to move to conclusions more readily than I used to.
So, I ask you. Is it possible for a young adult to "change" his or her type?
Regardless of your answer, I am still going to strive to become more "J" like in order to harness and categorize my environment.
PS - Don't give me that damned infjorinfp link. The woman who made is it batshit crazy.