Would you say, "I used to read books when I was 12, but then i grew up and stopped." or "I used to watch TV when I was 12, but then grew up and stopped."? They are pretty much the same thing but of course you wouldn't say that. So please don't speak down to us as if we are kids or even imply that anime and manga is for kids.
And please, growing up at 12? What a joke.