I often do the same thing. I'm an adult, and even I can see the VAST difference in my writing style and technique now as opposed to say... 10 years ago. I'm by no means prolific, but certainly even at one a year, you should see SOME change...

But I suppose that is the difference in some fic writers. Some of us write fic because it makes us creative, and we use it as an outlet to grow our skills. (Or in my case, we grow our skills because we want to do the fic verse justice... LOL) Others, just write because it amuses them and they have no interest in improvement.