I took an interest in music, art, and literature in my teens, and pursued them fairly actively (in both roles of participant and spectator). Those sorts of things were always more attributed to imagination and feeling, rather than analysis. Perhaps that simply gave those aspects of my personality a more frequent vent.
As for the relationship to other 4s and other INTJs, I'm afraid I can't give you much of an answer there. I'm not the most well-versed individual in enneagram, and I've only met one other person that I'm sure was INTJ (my calc professor). We're common on the internet, but far less common IRL.