Don DeLillo. (via) Echoing the Paris Review interview:

I wish I had started earlier, but evidently I wasn’t ready. First, I lacked ambition. I may have had novels in my head but very little on paper and no personal goals, no burning desire to achieve some end. Second, I didn’t have a sense of what it takes to be a serious writer. It took me a long time to develop this. Even when I was well into my first novel I didn’t have a system for working, a dependable routine. I worked haphazardly, sometimes late at night, sometimes in the afternoon. I spent too much time doing other things or nothing at all.