How old was Joseph when the 7 years of famine started?
To answer this question, you would need to perform some basic mathematics.
Joseph was promoted to second in charge by Pharaoh when he was 30 years old . The years of plenty were 7 years in length:
And the seven years of plenteousness , that was in the land of Egypt, were ended.
Genesis 41:53
After the seven years of plenteousness began the seven years of dearth:
Genesis 41:54And the seven years of dearth began to come, according as Joseph had said: and the dearth was in all lands; but in all the land of Egypt there was bread.
Therefore, to calculate how old Joseph was when the seven years of famine began, you would simply add how old Joseph was when he was prime minister of Egypt (30) to the seven years of plenteousness (7), which would mean Joseph was 37 years old when the famine began.