I can remember those essays at school when filling two sides of A4 seemed an impossibility. At university essays were supposed to be longer, though I'm not sure I ever achieved anything like the required length. My first short story was 400 words and I couldn't imagine how on earth it could ever be any longer. On my MA, I can remember gaily padding out my 3000 word essay with as many quotes as I thought I could get away with. (I only just managed to squeak a pass mark so I think they noticed.)
But now, nearly ten years of writing short stories and novels has left its mark. Give me a keyboard and I'll rattle off a couple of thousand words without a problem. Novels are about 500-700 words an hour, other writing - blogs, emails etc - is more like 1000 words an hour. Transferring words from my head to the page has become, with practice, a natural process. Writers write, and the more they write the more writerly they become. Just like my mother almost said.