[hugh]

I don't agree with your premise, here. You need to show any study that would demonstrate that women (a) really get fatter as they get older and (b) they get so much fatter that they would increase their BMI to the point of jumping up in the classification.

Four seconds of googling turns up: http://obesity1.tempdomainname.com/subs/fastfacts/obesity_wo...

see Table 3. The prevalence of obesity (as of 1999-2000) increases from 23% in the twenties to 42% in the fifties, and declines after that.