78. How old was Benjamin when his clan migrated to Egypt?

He was an infant.

We have a father, an old man, and a child [Benjamin] of his old age, a little one. Genesis 44:20

The lad cannot leave his father. Genesis 44:22

He was a grown man with ten sons.

And these are the names of the children of Israel, which came into Egypt. Genesis 46:8

And the sons of Benjamin were Belah, and Becher, and Ashbel, Gera, and Naaman, Ehi, and Rosh, Muppim, and Huppim, and Ard. Genesis 46:21