I started when I was 11, and was on again off again for roughly 5 years. This can be attributed to not having steady income, any patience, not having a rulebook, not having friends to play against/with and hating to paint. I got back into it 2 years ago, selling off my tau and going for chaos marines. I still hate to paint, so somethings never change.
I would quit for good if no one in the city played anymore, or if money became too big of an issue. Other than that, I'm pretty into it, even if i do procrastinate having a painted army.