Final answer:
The mother left Nigeria to attend university in the US at the age of 19.
Step-by-step explanation:
The mother mentioned in the provided references left Nigeria at the age of 19 to go to university in the United States. This information is gleaned from a personal narrative discussing the transition from life in Nigeria to encountering stereotypes and misunderstandings in the U.S., illustrating themes of cultural exchange, emigration, and the quest for education.