I shower once a day if I leave the house, and I never wear dirty clothes. This isn’t because I am fastidious, but because I am not, at all. I seem to totally lack the instinct that makes people dislike being dirty, and so if I don’t artificially control myself, I could slip into bathing once a week or less. And, I have greasy hair. One time in ten years I didn’t wash it before going to work (plumbing problems) and I had a kid ask me why my hair was so greasy.
But I can totally believe that some people can get away with showering once or twice a week.