How old was Jacob when Joseph was born?
The Bible does not explicitly state how old Jacob was when his son Joseph was born by his wife Rachel.
However, you can deduce how old he was by doing some simple math on several passages in Genesis .
For example, when reading Genesis 47:9 it states that Jacob was 130 years old when he came down into the land of Egypt .
You can deduce that Joseph was 39 years old when his father Jacob came into the land of Egypt .
Therefore with Jacob being 130 years old and Joseph being 39 years old, you can further deduce that Jacob would have been 91 years old when his son Joseph was born by Rachel.