Tolkien in a letter to W H Auden: I first tried to write a story when I was about seven. It was about a dragon. I remember nothing about it except a philological fact. My mother said nothing about the dragon, but pointed out that one could not say 'a green great dragon', but had to say 'a great green dragon'. I wondered why, and still do. The fact that I remember this is possibly significant, as I do not think I ever tried to write a story again for many years, and was taken up with language.
http://www.tolkienestate.com/en/writing/letters/letter-163-to-wh-auden.html