Yeah, exactly I was first introduced to type in college when I was 18 years old, (through the Please Understand Me book) and I scored as an INFP because it kept asking me if I preferred contemplating possibilities for the future or contemplating what's right in front of me. I was obsessed with two things at the time -- dating guys and creating art. Although I was happily taking lots of art classes, my love life was not as exciting as I wanted it to be, and I recall that my boring conventional boyfriend at the time wasn't fulfilling my dreams of what I wanted my "love life" to someday be like, and I kept choosing "future possibilities" on the test. I ended up with a score that was "N". I read the description of the INFP type and thought it didn't fit me at all, and dismissed type theory as being pop psychology fluff for years. I rediscovered it five years ago (I'm 37 now) and can more easily understand how the questions are hard to answer if you're not the type of person who easily notices patterns in either your past or present behavior. It seems to make a huge difference to SPs in particular what is going on in our lives currently at the time we're taking these personality tests.
Plus I agree with you about the youthful idealism thing -- Sensors have that too, especially those of us who prefer Introverted Feeling and who don't like the limitations that come with worrying about past standards or socially acceptable group norms.