This evening I came across this article on creativity that notes,
In middle childhood, kids sometimes create paracosms—fantasies of entire alternative worlds. Kids revisit their paracosms repeatedly, sometimes for months, and even create languages spoken there. This type of play peaks at age 9 or 10, and it’s a very strong sign of future creativity.
In our discussion of Peter pan I admitted to having an imaginary world I played in until I was probably 10 or so (I don't remember exactly when I stopped pretending the mouse paths in the bushes were the roads of a fairy town). Somehow it's comforting to know I'm not totally weird for having an intense imaginary life for as long as I did.