The turning point was when I hit my 30th birthday. I thought, if really want to write, it's time to start. I picked up the book How to Write a Novel in 90 Days. The author said to just write three pages a day, and I figured, I can do this. I never got past Page 3 of that book.
I think the worst and most insidious procrastination for me is research. I will be looking for some bit of fact or figure to include in the novel, and before I know, I've wasted an entire morning delving into that subject matter without a word written.