What age did your baby start to sleep (for the most part) through the night?

I have a three week old. He still wakes up every two to three hours for feedings and diaper changes, which I totally expect. Just can't remember about when our 2 year old started to sleep through the night. I want to say it was around 3 or 4 months old, but not sure. I know it's different for every child. Just trying to get a ball park figure. Thanks!