The Age of Jacob 
The Birth Year of Joseph

An Estimation of Ages and Seasons
 Biblical Astronomical Cycles

Although not specifically stated in the Bible,
it is possible to estimate Jacob's age at the birth of Joseph
from various Biblical passages.

According to the translation in the
Revised Standard Version of the Bible
"Joseph was 30 years old when he entered the service
of Pharaoh king of Egypt. And Joseph went out from the presence of Pharaoh, and went through all the land of Egypt." (Genesis 41:46).
 

Sometime shortly thereafter (anywhere from 0 to 7 years ?),
7 years of plenty are followed by 7 years of famine.
During the 7 years of plenty, Joseph stores grain,
so that we must presume some time for
the building of granaries, transport logistics, etc. and for the
installation of the infrastructure necessary for such stores,
since - later - in the period of famine
"Joseph opened all the storehouses." (Genesis 41:56)

When Joseph was visited by his brothers
the famine was "in the land ... two years".
(Genesis 45:6).
Shortly thereafter, Jacob and his family came to Egypt.
(Thus, in the 2nd year of famine,
Joseph was an estimated 39 - 46 years old.)

"And Pharaoh said to Jacob, 'How many are the days
of the years of your life' " (Genesis 47:8)
"And Jacob said to Pharaoh, 'the days of the years
of my sojourning are a hundred and thirty years;
few and evil have been the days of the years of my life,
and they have not attained to the days of the years
of the life of my fathers in the days of their sojourning.' "
(Genesis 47:9)

If Jacob is 130 here and Joseph is about 39 - 46 years old,
then Jacob was about 84 to 91 years old when Joseph was born.
Note that these are "days of the years of sojourning" (=seasons?),
as opposed to actual "days of the years of life".

If Jacob was 84 at Joseph's birth,
this gives an expected 2300 total "years" (23 x 100)
and 100 as the average for all 23 Patriarchs (up to Joseph)
for their "ages of sojourning" at the birth of sons.

If Jacob was 91 at Joseph's birth, then the total is 2307,
which is exactly divisible by 3 seasons  (sojourns?)
for a possible total of 769 years,
giving an average age of 33.43 for their fatherhoods,
whereas 33.33 results from the figure of 2300,
and 33 years are reckoned to a generation in ancient sources
(this is to be distinguished from the 19 years
of a generation reaching adulthood,
as reckoned by the Metonic cycle.)

Hence, there are two concepts of "generations" in the Bible
19 years to manhood and adulthood
but 33 years to fatherhood (in the idealized sense).
 

MAJOR BIBLICAL CYCLES
OF ASTRONOMY

The Metonic Cycle of 19 years was very important in ancient astronomy as was also the 33-year cycle. (See the links)

The system of heliacal risings found for the Patriarchs and Pharaohs is an "integrated" system of some kind first conceived and created at one location in toto prior to the deification of later historical kings, whose reigns, kingdoms or generations were then applied to the stellar phenomena. Much of the data seems to be ordered as a mnemonic device: Here is the evidence for this:

1.

The "lives" from Adam to Jared total 5514 for SIX patriarchs,
which is equally divisible by SIX to give 919.
Enoch is "inbetween" with 365 days as an intercalary leap year.

2.

The "lives" from Adam to Terah
i.e. the NINETEEN patriarchs prior to Abraham
totals 11571 which is exactly divisible by 19
(19 is the critical astronomical Metonic period) giving 609.
Is there an important astronomical calculation here? Yes.
We use both figures from above - 919 and 609 - as follows.
919 defective months x 29 = 26651
609 full months x 30 = 18270, so that we calculate
 26651+18270= 44921 days plus Enoch as a "leap day" = 44922.
If 44922 is divided by 123 years
this gives a value for the tropical (star) year of  365.22 days
(The closest ancient approximation was Hipparchus at 365.242 days.)

3.

The lives from Adam to Joseph for 23 patriarchs totals 12183
(the "gods" of the Sumerian city Kish are also 23).

If we subtract each of those 23 patriarchs as one intercalation or "jubilee" year from 12183 this equals 12160 which is exactly divisible by 76 (4x19 of the Metonic period).

If you add up the time elapsed from son to son for all the "sons" estimating Jacob's age at Joseph's birth at 84, and adding the life of Joseph, then the 23 patriarchs add up to a total of 2300 for their age at the birth of sons, or an average of 100 each at birth, i.e. 33.33 years - if we take 3 seasons as the measure of a year.