He also shares a good deal in common with Frog's teacher-figure, Nathaniel. Both grew up in Ohio. Both started their careers as physicists
An undergraduate major is not the same thing as one's career.
In Mama's case, majoring in physics while doing undergraduate studies does not justify referring to him as having 'started his career as a physicist.' To be precise, Mamas started his career as a veterinarian.
One becomes a physicist in the professional sense by becoming a researcher.
In the most precise sense, one has not embarked upon a career as a physicist until one has published articles describing ones original contributions in the field, usually after one has earned a Ph.D degree and found a position at a facility where one can continue to do research.