How short should men's shorts be?

What are the cultural rules in America these days for the length of men's everyday summer shorts? I prefer mine above the knee, but some people think it obscene. You NEVER see men younger than 30 with shorts above the knee. More questions; Don't dads with mid-calf shorts look stupid? ... like they're trying to look all gangsta and young? What is the proper length of shorts for a 20-year-old? A 40-year old? Is there a difference between white and black and Latino culture?

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