I am child free at the age of 47. I would say it is both by choice and circumstance. I do not hate children by any means, but I must admit that I am a very methodical person who likes to plan things. I thought that having children was a big responsibility and I wanted to have them at what I felt was the right time in my life. Honestly though, it was never a burning desire.
I ended up married at 27 and divorced by 33. I would say the divorce occurred right around the time I would have considered having children. My ex-husband had other plans. Anyway, by the time I recovered from the divorce, my mom having cancer, meeting my new husband and moving to a new city, children were no longer a priority. Plus my now husband is 11 years older than me. By the time we were married, I was almost 40, he was 51 and we just felt it was too late.
I have yet to regret my choice to never have children. Do I sometimes wonder what it would be like if I had a child? Yes, but I quickly can be thankful for what I do have.
This is really something that is different for everyone. There is no right or wrong answer.
I have to admit the worst part about being childless is the fact that some people really cannot understand it and ask too many personal questions or assume that I am some kind of freak for not having kids. Yet, I am to refrain from having any opinion about other people's children.
ETA: I also don't like the assumption that those that are childless are selfish or self absorbed. Some may be. However, there are plenty of selfish people who are parents or people who should have never had kids to begin with for a myriad of reasons..lol! Being a parent does not make you a superior person all the time.