My last gf dropped the b-bomb on me a couple years ago, and considering that we were both in our early 40s, I almost fainted. Seriously, there comes a point where it isn't realistic to become a parent, not only from the risks involved for the unborn, but that you no longer have the patience or stamina to be a new parent at middle age.
Niflheim, you are both right and wrong. When I was in my 20s, I raised a step-daughter and an adopted daughter. I loved them like they were my own, so I didn't feel that I had to have any more children in my life after the divorce. It wasn't until a month before my 40th B-Day that my first biological child was born. There are more risks involved for the unborn. I learned this the hard way when we lost the second child hours after her birth. A third child was born more than a year later. I can tell you that there is nothing in this world better than hearing "Daddy, I love you" coming from your childs lips. No matter how tired I am or how rough a day at work it was, hearing that always brings a smile and gives me a shot in the arm. As for patience, I don't just think, I know I have much more patience now than when I was in my 20s.