I can't recall the very first thing I read, but I do remember the first time I entered a (children's) library and was surrounded by books. It was the most beautiful place I had ever seen. After that, I read anything and everything. Mainstays during my childhood were Alcott's "Little Women" (read multiple times) and everything written by Judy Blume (also read multiple times).
I knew I was a writer in the second grade and by fourth grade, knew it was something that had merit when teachers started to take notice. I guess my teachers and classmates would have been the first readers of my writings. By sixth grade, some of the writing started to come from such a personal space that I didn't let many people, if any, read anything I wrote. That quote that states that writing is like opening a vein and letting your blood spill out onto the paper is right on!