I got my C64 (actually C64C) when I was 7, switched to a PC five years later just as I mastered BASIC and was starting to learn assembly.

To this day I can recite from memory a rough memory map, say which POKEs to do to switch background/border/text colors to my favourite scheme (white on black), and name the addresses of a few basic KERNAL routines.

Happy birthday, C64!