Genesis 5:32 make it appear that Shem, Ham, and Japeth were triplets and were born to Noah when he was five hundred years old. However, other Biblical evidence suggests that this was not so.
The flood happened when Noah was 600 years old (Genesis 7:11). Genesis 11:10 states that Shem was 100 years old when Arphaxad was born, and that Arphaxad was born 2 years after the flood. If Noah was 500 years old when Shem was born, and Shem was 100 when Arphaxad was born, then Shem had Arphaxad the same year as the flood and not 2 years after the flood as stated in Genesis 11:10, and therefore the idea that Shem, Ham, and Japeth, being triplets simply doesn’t add up to all the Scriptural evidence.
Therefore we need to dig deeper to find the interpretation of Genesis 5:32 that best fits everything that Scripture tells us. So when were Shem, Ham and Japeth born?
We know that Shem was 100 years old when Arphaxad was born 2 years after the flood (Genesis 11:10). The question then is whether this 2 years was calculated from the beginning of the flood (ie when they entered the ark) or from the end of the flood (ie when they had exited the ark). The best explanation to this question is to look at the date calculations in regards to Noah’s life. Noah was 600 years old when the flood started (Genesis 7:11), and was 950 years old when he died (Genesis 9:29), and we know that he died 350 years after the flood (Genesis 9:28). Subtracting 350 years from his age at death (950), takes us back to the age of 600 which was the year in which the flood started. Therefore we know that the Bible when giving dates in regards to the number years after the flood, is calculating the dates from the start of the flood and not the end of the flood. Therefore Arphaxad was born 2 years after the start of the flood when Noah was 602 years old. Therefore as Shem was 100 years old when Arphaxad was born, Shem was born when Noah was 502 years old.
All we know about the birth of Ham, is that he was the youngest son. Genesis 9:20-
From a process of elimination we then work out that Japeth was the oldest son, and it was him that was born to Noah at the age of 500 as stated in Genesis 5:32.
When was Shem, Ham, and Japeth Born