@kitten_tech

That really depends on what this person wants to "code".

I was lucky to start my teenage years with an Atari 800 and Atari BASIC (rev C).

There's a really good emulator that I run on Linux (atari800) which is reasonably easy to set up. That would give easy reach to a lot of the basics: graphics, sound, and a bunch of BASIC programs that can be examined to see how they work.