What did Nana mean by saying Ato don't talk with the foolishness of your generation?

Nana is reacting to Ato, as he attempts to correct her words... you do not correct your grandmother. We can also see this statement as ironic, considering that Ato has just returned from acquiring an education in the states.... in her eyes this makes him no different. In context, Nana has been questioning Eulalie's heritage, and the fact that she sees as as coming from "doubtful stock".... a child of slaves.