I actually haven't been bothered about grandchildren lately, which seems a little odd. I've been dating the same young man for almost five years, and around our first anniversary, my stepmother kept on pestering me about when we were going to get married and start having children, even though I had just turned 20 and wasn't through school yet. For the last two years, though, she's dropped it, though she has taken to hinting that I need to find a new gentleman friend - presumably one who will just marry and impregnate me already.
I asked my dad about it and he explained that she wanted me to start having grandkids when her first grandkid was new (he was born two weeks after my sweetie and I got together), partially from the excitement of grandbabies and partially because she thought Dad would be more active with grandbabies if he had a biological one. This is ridiculous, because my dad is indifferent to babies. He's exceedingly fond of my stepsister's son now that he can talk and play, but until then, he just didn't really care. He's done the same with my stepbrother's child and with my stepsister's other child - he'll hold them and smile when they're babies, but he likes them better when they're children. I have no reason to believe he will be any different with a blood relative.