When was Shem born?

Hi ... I came across this site while doing some research for my bible timeline.I hope no one minds me adding my 2c worth...but I thought this might be a bit use full...In Gen 5 ... as every one reads ... Noah had 3 sons when he was 500. The list is Shem, Ham, and Japheth.And in Gen 11 ... we read that Shem was 100 and begat Arphaxad 2 years after the flood.The confusion seems to be around the fact that Shem is listed first in Gen 5 ... indicating that he was the first born.However ... in reading Gen 10 ... we find the answer ... the generations of Shems sons ... we find that Japheth is listed first with his sons .... and we read in Gen 10:21 that Japheth was the elder.As has been correctly pointed out in one of the earlier answers to this question ... Noah was 600 when the flood occurred ... and 601 when the flood ended ... meaning that the flood was on the earth for a full year...therefore ... Shem had his son 2 years after the flood .... meaning
Noah was 600 ... + 1 (year of flood)... + 2 (years after the flood).At this time Shem would have been 100 ... meaning that Shem was born when Noah was 503.We have a similar situation with Abraham ... although he was listed first of the 3 sons born to Terah at age 70 ... we read in Gen 12:4 that Abraham was 75 when he left Haran. We also note in Gen 11:28 that Haran ... brother of Abraham died before Terah left Ur of the Chaldees.A comparison of prophetic time periods would indicate that the call for Terah to leave Ur of the Chaldees had happened at least 50 years earlier.And Acts 7:2-5 clarifies this issue further by indicating that the call for Abraham to come out of Ur happened in 2 steps ... firstly ... with his family they moved to Haran ... and then out of Haran ... after the death of his father.I hope this helps to answer this question.