Same here. Even had an 8-note keyboard-driven music player built in, iirc. Although it lead to a life-long interest, I never really wrote anything 'serious' from scratch since then. Scripts and editing others' code was about my limit.
And this is despite trying at 12-13 to 'go pro' with Visual C++ ordered through a student discount and the C++ For Dummies book (I had no idea where to start) that never took off the ground. A wish there was a local group or mentor I knew about back then!
At the time (I was probably 11 or so) I knew that it was important to learn to write serious stuff, and knew that an operating system was probably "serious stuff," and so I thought it might be a good learning experiment to write an operating system in QBasic. Needless to say I was missing a few links in how "serious stuff" was written back then, but it sure was a fun intro!