What Genesis actually states
After Isaac entreated the LORD for Rebekah, she conceived and bare twin sons. Esau came out first, and his brother Jacob followed, taking hold on Esau’s heel. The text then says Isaac was threescore years old when she bare them.
Jacob’s birth is therefore dated relative to Isaac’s life, not by a year such as “2006 BC.” Different long chronologies of the world attempt to convert patriarchal ages into calendar years, but those systems go beyond the plain statement of Genesis 25.
How Jacob’s birth anchors later ages
Because Isaac was 60 at Jacob’s birth and later died at 180, Jacob was 120 at Isaac’s death. Because Jacob entered Egypt at 130 and died at 147, the whole timeline of Joseph’s life can be coordinated with Jacob’s age.
Questions such as “when was Joseph born” in everyday language often want either a calendar year (not given) or Jacob’s age at Joseph’s birth (about 91). BibleAV answers both kinds of intent by distinguishing what is stated from what is deduced.