What you said brings up a point I don't see above: some skills transfer. Your early dance skills transferred so that you had a head start on the later forms. I've seen a similar thing when I've coached rowing: people with a background in something like dance or martial arts or fencing, where they've had to control their body precisely are much faster at learning the basics. On the other hand, once they get past those to an intermediate level, just like anyone else they have to work like hell to build strength, endurance and skill if they want to be really competitive.

Where this relates to writing is *reading*: a dedicated reader already has a head start on seeing how words and patterns build and relate to form a story, certainly over someone who is just starting without having spent years drowning in words at every opportunity. Maybe that cuts out the first 250,000 words of crap. Or maybe the skilled writers commenting above, who are themselves dedicated readers, have already factored that in and it would be many more than a million words of crap for a wannabe writer who is not already enmeshed in other people's words.