I know from some of the clothes I've hung on to from yesteryear that I've been a fair bit smaller in my adult life than I am now.
I have a size 14 pencil skirt from the mid 90's which used to be quite loose then, but is at least a couple of inches too small to even do up. I didn't really weigh myself much back then, so I don't know what I was, but probably in the 9's!
If I was, I have no ambition to get back there. My face has just about survived gaining and losing all the weight, but I'm in my mid-forties, and I would be risking looking very haggard if I were to take my weight that low I suspect. Plus, if I couldn't sustain that weight then, I almost certainly couldn't now that I'm 20 years older and everything is starting to slow down.
I'll settle for a BMI at or around 25 - anything less would be a bonus.