Although the three sons are consistently listed as “Shem, Ham and Japheth,” there is some uncertainty as to their relative positions according to age. The fact that Shem is mentioned first is of itself no definite indication that Shem was Noah’s firstborn, since Shem’s own firstborn son (Arpachshad) is listed third in the genealogical records. (Ge 10:22; 1Ch 1:17) In the original Hebrew, Genesis 10:21 allows for more than one possible translation, some translations referring to Shem as “the brother of Japheth the oldest [“elder,” KJ],” while others call him the “elder [“older,” AT] brother of Japheth.” (AS, Dy, RS, JB, Ro) The ancient versions likewise differ—the Septuagint, the translation by Symmachus, and the Targum of Onkelos present Japheth as the older, while the Samaritan Pentateuch, the Latin Vulgate, and the Syriac versions place Shem as the older brother of Japheth. The weight of evidence found in the rest of the Bible record, however, indicates that Shem likely was Noah’s second son, younger than Japheth.
The record shows that Noah began to father sons after reaching 500 years of age (2470 B.C.E.), the Deluge occurring in his 600th year. (Ge 5:32; 7:6) Already married at the time of the Deluge (Ge 6:18), Shem is stated to have fathered his first son, Arpachshad, two years after the Deluge (2368 B.C.E.) when he, Shem, was 100 years old. (Ge 11:10) This would mean that Shem was born when Noah was 502 years of age (2468 B.C.E.); and since Ham appears to be referred to as the “youngest son” (Ge 9:24), Japheth would logically be the first son born to Noah, when he was 500 years of age.