Sort of. I created an imaginary older brother named Steve when I was in 2nd grade.

I'm the oldest in my family. Up to a certain age, I couldn't understand why my parents couldn't give me an older brother instead of the 2 younger ones I had. So I created Steve. I'd tell my friends tales about him and cool stuff he did. Then I somberly told them how he'd died in a car accident a few years earlier. This stirred sympathy and sadness. I was pretty impressed with my ability to create such a convincing whopper.

My parents overheard me tell a friend about Steve one day. I found this out decades later when a friend of my mom's lent me a binder of old letters Mom had sent to her when we lived overseas. My mom told it as a funny story about how she & my Dad had to work hard to stifle cracking up when they heard me in the next room going on and on about Big Brother Steve.

I think this was my first bona fide attempt at creating fiction. About 15 years later I went on to earn a Master of Fine Arts degree in what else? Fiction writing.