Before you ask, I was 12 when I drew the first one (so now you can all do the math and figure out how old I am).
WHOAH. I am really impressed by your improvement- you have such a modern-looking style, I could have sword you were my age. (I'm the same age as Lady Gaga! That's my hint. XD She's also not the age most people would assume, though...)
I'm also really amazed that you've been working on the SAME STORY since your were 12! I would never have that much patience or dedication. You deserve some kind of award or something. O_O
As for my own progression, I recently did that "art improvement meme":
But if you're interested in seeing how the "Sister Claire" style has evolved, check out this really old concept art:
You can see the refinement the comic's style has gone through if you compare those designs to a recent drawing of Claire: