Look no further than Sarah, barren at 90, and, told by God, YOU, my child, will have a kid. Moses laughed, surely, the whole Israel nation laughed. But WHO had the last laugh? God. And, Sarah, because she had faith in God, never doubting Him.
See, there's that Veggie Tales episode where they quote the verse "With God all things are possible." Larry says "Well I've always wanted to be a chicken. Do you think God will make me into a chicken?" No of course not. It may be possible for God to make Larry into a chicken but He made him a animated talking cucumber, because that's what He wants him to be. It should never be an issue of whether or not God is able if we know that God can do everything. The issue is always whether or not God is willing. And He's not often willing to do what contradicts the way He made something. So for God to make Larry into a chicken would esentially be God chaning His mind about who He wants Larry to be. Does that make sense? So, God gave Sarah (and Elizabeth) babies in their old age because the babies they had were very, very special. But, for the rest of us, he made women in a way where our fertility goes down at a certain way. He does not usually give babies to women who are in their late 40s and early 50s for a good reason. So, if one doesn't get married until then, we have to confront the fact that God will not likely give them the gift of children. Do you have any idea how painful that is for a woman who's always wanted children???