I'm 45, no kids, by choice. It's not because of my career, it's just because of the life I choose to live. I would simply not live a single day of my life the same if I had children. I do live every single day of my life as I choose (and like).
If you have kids, you don't have that choice anymore. You can adjust your needs, your expectations to the presence of kids... but it's a different story, isn't it?
For me, it's all about freedom. YMMV