(Genesis 12:1) Now Jehovah said to Abram, “Go out from your land and from your relatives, and from the house of your father, to the land that I will show you.
After Terah, Abram’s father, died, Abram is commanded to leave Haran.
(Genesis 11:26) When Terah had lived seventy years, he fathered Abram, Nahor, and Haran.
When Terah was 70, Abram was born.
(Genesis 11:32) And the days of Terah were two hundred and five years, and Terah died in Haran.
Terah died at the age of 205, which would make Abraham 135 when he left Ur.
(Genesis 12:4, ASV) So Abram went, as the Lord had told him, and Lot went with him. Abram was seventy-five years old when he departed from Haran.
Here we see that Abram was only 75 when he left Haran.
Discrepancy: According to 11:32, Terah died at the age of 205; hence, Abram must have been 135 when he was called to leave Haran. However, 12:4 says that he was only 75 when he left Haran. The Source Critic informs us that this seeming contradiction is resolved if Genesis chapter 12 is of a different source from the genealogy of Genesis chapter 11.
The above need not be a contradiction at all. True enough, it was at the age of 70 that Terah began having children (Gen. 11:26), but does Abraham have to be the firstborn child simply because he is listed first? Ask yourself, what weight do the names Nahor and Haran play in the Bible account? Now ask yourself, what about the name Abraham? He is considered to be the father and founder of three of the greatest religions on this planet: Judaism, Christianity, and Islam. He is the third most prominent person named in God’s Word. This practice, that of placing the most prominent son first in a list of sons even though they are not the firstborn is followed elsewhere in God’s Word with other prominent men of great faith, for example, Shem and Isaac. (Gen. 5:32; 11:10; 1 Chron. 1:28) Therefore, let us keep it simple. Genesis 11:26 does not say that Abram was the firstborn; it simply says that Terah began fathering children, and then it goes on to list his three sons, listing the most prominent one first. Thus, it is obvious that Terah fathered Abram at the age of 130. (Gen. 11:26, 32; 12:4) In addition, it is true that Sarah was Abram’s half-sister, not by the same mother, but by having Terah as the same father. (Gen. 20:12) Therefore, it is Haran, who is the firstborn of Terah, whose daughter was old enough to marry Nahor, another of Terah’s three sons.―Genesis 11:29.