I grew up in the day where your ideal body weight was 100 pounds if you were 5 foot tall and 5 pounds for every inch over that. So, at 5-1, my ideal weight was 105, which was pretty close to what I weighed through high school and college. I still mentally calculate what people “should” weigh using that formula.
The newer guidelines, including BMI, are much more liberal. At 128 pounds, I’m in the “normal” range, even though I could still easily lose another 10 pounds and be nowhere near too thin. At 105, though, I probably would be too thin, although that’s what my mom weighed for many years. But she was also a smoker and, of course, I’m bigger boned( aren’t we all lol?)