1. By reading the source code of tape programs and magazine source listings. The BBC Micro boots to a command prompt and has Basic in ROM, so that was fairly helpful... and from then on for other languages, self-taught by viewing source code.
2. As soon as i could! (aged about 7)
3. My second job, after 3 months of hell in telesales.
So he was wrong then? NS6/firefox seems to be doing alright today...
Rewriting your OWN codebase from scratch certainly makes it get better with each iteration - as long as "from scratch" implies constantly referring to the old code.