I can't speak to other times and places but in silicon valley in the late 1980s I went to a temp agency and looked for unskilled work during the summer - I don't think I ever came across any jobs that paid as low as minimum wage. One summer I was a "shipping clerk" (meaning: guy who gets stuff out of a warehouse and puts it in boxes) at Syva - that paid over twice the minimum. Another summer I did data entry for the Accounts Receivable department at Dialog - that also paid much more than the minimum, and required only rudimentary typing skills. And yes, naturally once I was a declared CS major I could intern at IBM, but even before that I didn't see a need to work minimum wage.

(Even McDonald's was paying more than minimum in my area.)