I have always found this interesting, it seems for folks in their 20s and 30s having kids leads to more travel and fun. However, as these folks age into their 40s there begins to be a shift as there are less life milestones to look forward to and the question about "what is my legacy?" begins to creep in.

I think everyone makes their own choices for their own reasons, but this is just my observation, people in their 80s love having grown kids and grandkids around so they don't simply slip off into the abyss upon death.