I will be the baby of the family! Most of the other homestay families also have adult children, and experience with foreign students. Several have maids that take care of the house. Mermoz is, as I said, one of Dakar's wealthiest neighborhoods.
I should also add that it is commonplace--perfectly normal--for children to live with their parents until they get married. In the case of young men, they often live with their parents until they have enough money to marry, because they must be able to afford a bridewealth (money paid to the family of the bride, in order to compensate for the loss of a daughter--or, if you're more cynical, to buy her).
Earlier today, a friend of the family called, named Anne. Anne is an older woman--bright, kind, and curious. She was very excited for me and the opportunities that young people get to have "these days," but she was a little worried that I might be staying in a thatched hut. I explained that Dakar is one of the most Westernized cities in one of the most Westernized countries in Africa--as well as being thoroughly cosmopolitan, tolerant, and hospitable--and that I would be staying with an upper-middle class family. Anne was relieved.