I want to have kids someday, but want to ensure I'm in the right position, financially, emotionally, and relationship wise before I do so. I do believe in some planning, but I also like to think its good to keep some magic in things and have a few surprises every now and then.
The irony is that a couple of century's ago I know of 17 year olds marrying 13 year old wives and starting familys. Obviously life expectancy was much shorter back then. People living to their 30's or 40's at most. Simple health problems that are cured easily today killed many people back then as well.
It's just interesting how with prolonged life, society's views of maturity, marriage, and procreation change.