I started on my casio when I was 12 ish back in the early 90s, and it was great for me cause I suck at graphics. Instead of pixels, the only output I could use were chars on the calculators grid. Something like 6 rows, 12 columns, like: ^ is your ship, * is the bad guys, and I is a laser. Games I remember making were - going through a tunnel avoiding walls that get progressively narrower - something like space invaders - snake of course - and some specific stuff to make fun of my teachers.