I took two official MBTI tests, one when I was 22 and the other when I was 25. I tested INTJ both times, but T/F and P/J were both borderline. However, as I passed through the second half of my twenties, I became much more stable and comfortable with myself, and when I took some on-line tests, I test as INFJ 100% of the time. The descriptions also fit me better than INTJ.
However, now that I know I am INFJ, I feel confused when I start using functions other than what they tell me I normally use, Ni/Fe/Ti/Se. Now that I can recognize them, I am more confused, which may be why so many people find themselves questioning their type.
Anyhow, some days I feel INFP, some days INTJ, some days I feel like a super extravert (but those days usually end in me suddenly withdrawing into a book or solitary project). I guess MBTI can only explain a small fraction of what human beings are really made up of.