It is common for women who are gaining weight to not realize that they cannot dress the same as they always have before.
As a man, the same thing happened to me. My brain did not comprehend age. I thought I was the same guy that I always was.
It was only when other people started pointing out to me very explicitly, 'Hey man, you cannot dress like that anymore.' did it finally register to my brain that I had become a middle age Dad. Only then did I switch to Khakis, sportcoat with a hat. I finally made the step-up and evolved into dressing for my age. It did actually make me more acceptable to people in my new age bracket.
The same epiphany has to happen to women as they gain weight. One of the most sad things I have ever seen while shopping was a middle aged woman of substantial proportion dragging two children with her while wearing nylon short-shorts with the word 'Juicy' plastered over her butt. I mean come-on Lady, wake up already. Obviously in her mind she still thought she was in her twenties. Just like I used to think.