I had a spectrum, and found a comic shop that had old 80s computer magazines that taught assembler. I also found a z80 compiler via obscure pen pals via small ads in the games magazines. Edge of the seat stuff, but the feeling of accomplishment was astonishing when you actually did something. I think the bar is so high for bedroom coders these days and they're always getting weird drag n drop languages pushed at them, which just stifles creativity (imho).

I had that exact experience. I was playing Half-Life (1998) and I learned that you could download the source and modify it (I was not a programmer, just some little kid with a computer). I somehow figured out how to download a free/trial of Borland C++, setup my dev environment, and recompile the entirety of the source code after making a one-character change (changed the friendtype of grunts from one integer value to another) so that they would treat the player as "friendly" and focus on shooting aliens instead. It was a very painful process.

This was before Half-Life: Opposing Force was released.