Although at my age I have no intention of having my first child, I'm still fertile enough to technically get impregnated. I know that sooner rather than later menopause will set in, and my fertile days will end. I know I'm being unrealistic, perhaps even silly, but I cannot accept the onset of infertility. The computation of how long I have before that dreaded thing happens makes me very agitated and nervous. .
It is a gradual thing, not a countdown. A couple of years ago I read about a women in Britain that had a child at 67. Alas the risk of pregnancy complications rise gradually too, so you best hurry up and find a stud.