I think there is a huge difference between 'thin" and healthy.
Obviously, height plays a massive part.
I'm now a size 16, I'm 5'8. I'm in proportion.
Likewise, from 13 to 24 I was incredibly skinny, very much in with the thin look of the late 90s, hips out, flat tummy, flat chested.
I did have anorexia in my mid to late teens, and used to stupidly compete with someone I thought of as a mate at sixth form to not eat most of the week bar fruit.
I then had my DD when I was 25, probably looked the best ever, as I was breastfeeding, suddenly had huge boobs, but was slim and a healthy weight. All went downhill when I had DS and he was incredibly early and I couldn't breastfeed but had gotten used to eating what I liked which was a novelty to me whilst pregnant and breastfeeding. I went up to a size 18/20 and felt unwell with it, alot was stress eating and I was on strong anti-depressants following a breakdown.
I'm OK with how I am but keeping an eye on it as I'm now peri-menopausal and know that that can cause weight to pile on my middle.
If I could be any size I'd prefer a 14 but also like my boobs!