I'm in much the same position-- I've been writing software for about 30 years, but never as my main job, sometimes for fun/entertainment and sometimes for work.

I often set code aside for months or years as I don't have time to work on it or get distracted by something else. I fortunately wrote some stuff in Turbo Pascal about 25 years ago (a Corewar implementation, fwiw) that I liked, and then went back to about a year later and tried to read. My reaction was "Wow, did I write this?". Even though it was broken into decent sized functions and they were labeled and lightly commented, I hadn't really explained anything at all of what was happening and why, and it took a long time to figure out.

I now tend to write for my future self, knowing that I'm not going to remember any of it: Start with comments to describe what the program is going to do at each step, write the program, describe what it's doing and why as a I go. If it operates on external data that might change, I'll put in notes of what it's expecting.