I just remembered sth from my childhood (abt 12yrs old)
I had a book full of maps of different countries and I was a fan of "empire games", those games that you're a king, you fight and expand your territory. I was more comfortable playing alone so I had a paper with my soldier count and budget on it and used a long ruler as my weapon (sword or gun), fighting with imaginary opponents. Each game happened on a specific map and I was constantly updating my territory after each war. There were different variations of the game (modern time vs ancient, starting as a prince and inheriting the crown vs starting as an ordinary person, happy vs sad ending, etc) and I would keep playing each for a week or two. It was played in my parents room or in my room when nobody was there and it happened a lot that my mom scolded me for jumping on the bed. Sometimes it had a bit of romance taste to it as well.
The very same game setting was also of my interest when I was a super hero doing different things having different super powers. I was again playing it alone in my parents room with different scenarios and variations.
In those years I had another game I remember which had a similar nature. I used to draw a small store on a paper and working hard to expand my business. Still my budget on the paper, my inventory size too. Still alone and when my brother asked me to join I rejected. However later we played the same thing together and I cheated a lot to be superior than him in the game. I rent 'myself' as a car to my brother to earn more money; I was carrying him on my back!
I used to play with him a lot and I don't know when was the "I prefer playing alone" time point. I even remember that in some cases I was insisting and even manipulating him into playing with me when I was ten or eleven.
What a childhood.
P. S: just wrote whatever came to my mind with no proofreading. Any mistakes? Cut me some slack