I don’t think they’re implying it takes 21 years to learn. I’m inexperienced and learned how to accurately follow paths with bezier curves using the same technique after watching a 10 minute Burt Munroy tutorial.
Correct. I have certainly learnt a ton more about how to manipulate vector art in the intervening years, and the set of tools I have available has expanded a lot - Adobe's added a lot of tools to Illustrator, and so has the Illustrator plugin ecosystem. But those three simple rules did a lot to make my Illustrator practice a lot faster.