I'll admit that it might have been somewhat of a lifestyle for me when I was six, as that was around the time the Turtles were, like, EVERYWHERE!
Nowadays, I'd call it more of a fandom. Plus, I'm not quite as into the '87 toon (what got me into TMNT way back when) anymore, but I do enjoy the Mirage comics, the 2k3 toon (except for Fast Forward and Back to the Sewer), and the movies (except for the third one).
Ya, I don't really eat, sleep, and breathe the Turtles, but it is definitely a big fandom of mine.