I'm a 5'-10" 73 year old male. My IBW based on four models is shown below. I'm currently over 190, so 30 pounds to shed to reach the highest IBW. But, I do know if I actually hit 165, I'd be skin and bones and look terrible, same as you describe your friend.
When she told us she’d lost 70 lbs, well, I was surprised, because she never looked like she was that overweight for her height. I’m guessing she’s 5’5” or 5’6”. She’s lost it all over but it shows most in her face. She looks very withdrawn. I’m not sure what it is, but she looks much older, not younger.
I dont know where they are getting those ridiculous numbers.
Mine claims that I should be lighter than when I wrestled in high school and about 30lbs lighter than what the military expected. Of the weights they give as correct one is not only 30lbs lighter than what I wrestled, no I wasnt the chubby kid that just showed up, but there was no one on the team, not even that skinny spaghetti kid, that was making those weights without going to extreme ends at that height.