what age did you start a bedtime?

Our daughter is 3 weeks today. Most nights she's doing a 3-4 hour stretch, then waking up for a feeding that lasts anywhere from 30 min - 2 hours, and then goes back to sleep for another 3-4 hours. She's not going to bed until 11 or so though. I'm not sure when to start putting her to bed earlier. Every site I read gives a different age!