Scripture, Genesis chapter 11 and verses 10 and 11:
“This is the book of the family of Shem. Shem was a hundred years old and became the father of Arpachshad two years after the flood. After he became the father of Arpachshad, Shem lived five hundred years and became the father of sons and daughters. “
Noah and his family
When Noah was five hundred years old, he became the father of Shem, Ham and Japheth. Japheth was probably the firstborn of Noah’s three sons and could have been born when Noah was 500 years old, about 50 years before Noah started to build the Ark. Shem was born when Noah was 502 years old. Many believe that it took Noah 100 years to build the ark, however that is not true. When God spoke to Noah about building the ark, Shem Ham and Japheth were already grown up and had wives. The time Noah and his family spent building the ark could have been approx. 50 to 70 years.
I will now go through Sem’s family up to Abraham; Shem was 600 years old and got Arpachshad when he was 100. Arpachshad got Shelah when he was 35 and became 438 years old. Sjelah got Eber when he was 30 and became 433 years old. Eber got Peleg when he was 34 and became 464 years old. Peleg got Reu when he was 30 and became 239 years old. Reu got Serug when he was 30 and he became 239 years old. Serug got Nahor (Abraham’s grandfather) when he was 30 and became 230 years old. Nahor got Tarah when he was 29 and became148 years old. Tarah became the father of Abraham, Nahor, and Haran the firstborn. Tarah became 205 years old.
Noah became 950 years old, his son Shem 600 years old, and we see that the age of the family gradually decreased to between 140 and 200 years, Abraham, for example, became 175 years old.