I'm not sure about other people out there, but for me, I'd really like to know how my parents grew up, and what made them what they are today. For me, it is not easy to just approach my dad and ask him, "When did u hit the important career moment?" or "What were your interest in school?" and things like that, because our relationship has established itself to be more of a barrier-ed father-son relationship that's open only for adult talk, and not personal talk.
For me, an auto-biography should be written at every milestone in life, similar to the milestones I've written in previous posts. That is, to write about your youth and education life when you start working... and date it. Meaning, the topic can be "Javalier: 1970 - 1990. Written 4th Jan 1992, completed 24th Feb 1992." Nothing wrong with that, maybe when you reach 45, you'd look back at the post and you can add comments, and also date that comment, so that you can see how things have changed in perspective of age. Never ever edit again when that chapter is completed.
After your first kid is 10 years old (not another chapter at marriage, as you'd have too little to write about). At this time, you can talk a bit about your career, what you faced, what you did right and wrong, what you think you should have done otherwise, and also include your marriage talk, your relationships, etc, as well as "where and when" of important events especially for the understanding of your children. Still, the story should still center yourself.
When am I going to start writing my own? I'm not sure. All I know is it should be a one straight off, no need to draft and re-drafting. I'm not trying to market myself, I just want a summary of my life.