Initially when I was starting out Lucid Dreaming, I was around 9-10 years old. I didn't have a defined Paracosm just yet, but I was determined to make one as I further learned how to lucid dream.
And in all honesty, I still don't really have a proper one yet, or at least not one that lasts long.
The real question is,
Well, I'm glad you asked!
A Paracosm is a fictional world that someone creates or shows through creative mediums.
For example, the mediums I express my paracosm through are lucid dreaming, writing, and doodling.