Genesis 12:4

So Abram departed, as the Lord had spoken unto him
Or, "when the Lord had spoken to him", as Cocceius renders the words; when he had called him a second time, even when in Haran, immediately after the death of his father Terah; as soon as ever the words were spoken to him before recorded, he immediately prepared and got all things ready for his journey, and departed from Haran, as he had done before from Ur of the Chaldees:

and Lot went with him;
of his own accord, and he only, besides his wife Sarai and his servants, for Terah was dead, and Nahor and his family stayed behind.

And Abram was seventy five years old when he departed out of Haran;
by which it appears, as has been observed, that he was not Terah's eldest son, born when he was seventy years of age, ( Genesis 11:26 ) for then he must have been at this time, one hundred and thirty five years old, since his father, who was just now dead, lived to be two hundred and five years old, ( Genesis 11:32 ) so that Abram must be born in the one hundred and thirtieth year of Terah: how many years before this time he was converted from idolatry cannot be said with any certainty; various are the accounts given by the Jewish writers; some say that at three years of age he knew his Creator; others at eight; others thirteen; others more probably when forty; others fifty one; others fifty two; and others say he was sixty years old when he began publicly to assert the unity of God in heaven ^F26: however, all agree it was before the age here mentioned, as it may well be concluded.