I don't think it's gross to only shower 4 times a week, unless you're a particularly sweaty person or are very physically active. If it gets to the point of others telling you you need a wash, though, it's clearly quite necessary.
My mum's always only showered every other day, and she looks immaculate. Never in my life have I seen her sweat, and she's never smelled anything other than perfectly nice.
That said, her behaviour did cause some difficulties for me growing up, as it seemingly never occurred to her that I might be different to her, and require more cleaning. She thought daily showers were excessive, since she didn't need them. From the onset of puberty (aged 10) until about 15 I suffered badly with excess sweating, as well as greasy skin and hair, but only showered every other day, sometimes only a couple of times each week (especially when I developed depression and anorexia). Nobody ever told me I smelled, but I suspect I must have. I know I was obviously sweaty, and it causes me a lot of embarrassment to think about that time in my life. If I have children, teaching them good hygiene will be very important to me.
I shower twice a day now, as I do a lot of exercise. I'm only in the shower for 3-5 minutes, unless I'm washing my hair.