Eight years together (3 married) and neither my husband nor I want kids. That was our agreement from the get-go and nothing's changed.
I just have no interest in kids, no interest in parenting, no interest in the actual birthing process (yikes!) and no maternal urge around kids.
Like the OP, I didn't come from a big "kid" family. I (at 27) was the youngest person in my family until my sister had a kid a year ago. Also, my husband and I are selfish and want to spend money on ourselves, go out, go on vacations, and not plan life around kids' schedules.
As for the regret issue others have brought up-- wouldn't you rather get to that point 20 years in the future and regret not having a kid than get to that point and regret HAVING one?