"Then Abraham fell upon his face, and laughed, and said in his heart, Shall a child be born unto him that is an hundred years old? and shall Sarah, that is ninety years old, bear?"
Why would Abraham doubt the ability to have children at over 90 years old when it happened all throughout history leading up to him. In genesis 5 we see this geneology.
3.And Adam lived an hundred and thirty years, and begat a son in his own likeness, after his image; and called his name Seth:
4 And the days of Adam after he had begotten Seth were eight hundred years: and he begat sons and daughters: 5 And all the days that Adam lived were nine hundred and thirty years: and he died.
6 And Seth lived an hundred and five years, and begat Enos:
7 And Seth lived after he begat Enos eight hundred and seven years, and begat sons and daughters: 8 And all the days of Seth were nine hundred and twelve years: and he died.
9 ¶ And Enos lived ninety years, and begat Cainan:
10 And Enos lived after he begat Cainan eight hundred and fifteen years, and begat sons and daughters: 11 And all the days of Enos were nine hundred and five years: and he died.
12 ¶ And Cainan lived seventy years, and begat Mahalaleel:
13 And Cainan lived after he begat Mahalaleel eight hundred and forty years, and begat sons and daughters:
14 And all the days of Cainan were nine hundred and ten years: and he died.
15 ¶ And Mahalaleel lived sixty and five years, and begat Jared:
16 And Mahalaleel lived after he begat Jared eight hundred and thirty years, and begat sons and daughters:
17 And all the days of Mahalaleel were eight hundred and ninety and five years: and he died.
18 ¶ And Jared lived an hundred sixty and two years, and he begat Enoch:
19 And Jared lived after he begat Enoch eight hundred years, and begat sons and daughters:
20 And all the days of Jared were nine hundred sixty and two years: and he died.
Genesis 11 has more old guys having children.10 These are the generations of Shem: Shem was an hundred years old, and begat Arphaxad two years after the flood: 11 And Shem lived after he begat Arphaxad five hundred years, and begat sons and daughters.
12 And Arphaxad lived five and thirty years, and begat Salah:
13 And Arphaxad lived after he begat Salah four hundred and three years, and begat sons and daughters.
14 And Salah lived thirty years, and begat Eber:
15 And Salah lived after he begat Eber four hundred and three years, and begat sons and daughters.
16 And Eber lived four and thirty years, and begat Peleg:
17 And Eber lived after he begat Peleg four hundred and thirty years, and begat sons and daughters. 18 And Peleg lived thirty years, and begat Reu:
19 And Peleg lived after he begat Reu two hundred and nine years, and begat sons and daughters.
20 And Reu lived two and thirty years, and begat Serug:
21 And Reu lived after he begat Serug two hundred and seven years, and begat sons and daughters.
22 And Serug lived thirty years, and begat Nahor:
23 And Serug lived after he begat Nahor two hundred years, and begat sons and daughters.
24 And Nahor lived nine and twenty years, and begat aTerah:
25 And Nahor lived after he begat Terah an hundred and nineteen years, and begat sons and daughters
Why would a guy living during a time when people lived hundreds and hundreds of years think it was weird that he would have a child at 100?