If my metric waist size was half my height, I would fall into the category of being high risk for heart disease, as it would be over 80cm!
And if I had a waist size as large as 80cm, I would also have a double chin, a fat arse and cellulite. Healthy shmealth!!!y. I wanted to look good. And I dont look good at 180lb! I'm 5ft 10 and 140lb at the moment and I like that MUCH better. The stupid nutritionist I saw told me I'd never get to 154, I was being totally unrealistic. My doctor never mentioned a goal. I guess your goal depends whether you're a "I just want to be healthy" type or a "I want to be hot" type. I was/am way more the second type and I dont believe age has anything to do it, as I'm 44.
The only thing I noticed, I got a bit thinner after chemo, and was down to a BMI of 19/20. This is not actually underweight, its the very bottom of my healthy range though. My fill doctor (not my surgeon) was really funny about it, she wouldnt give me my fill back after being totally empty for the surgery, she really wanted me to gain weight. WTF is with everyone being so afraid of not having meat on your bones? If I'd dropped even lower, sure, once you're underweight you do need to gain. But what was wrong with wanting to stay at a BMI of 20? I couldnt by the way, once chemo finished and I regained some health, I gained 10lb pretty quick even WITH Fluid in my band.
Let your doctor set you a goal if you like, then if you're anythign like me, just ignore it and do whatever the hell you want. I know the difference between medical advice I need to listen to and medical "opinion" that I can ignore if I choose. You can weigh whatever you want. Dont be afraid to shoot for a low weight if you really want to, you dont know till you get there whether its maintainable, or whether it will look good. I feel a bit yuck because I've gone back to 140lb from 130 - but heck, I'm 5ft 10, it was pretty darn skinny. But I'd rather feel a bit fat and flabby from having gained so much weight, lol, than to have never experienced it. I know now its not maintainable for me, its too hard and takes sacrifices I'm not willing to make. And that $300 pair of jeans in my cupboard that fit me for 5 minutes can go on ebay where they wont mock me!
Likewise if you want to remain a bit heavier in the technically overweight cateogory, then remember there's a lot more to health than your actual weight. You've added years and years onto your life and improved your quality of life by losing the bulk of that weight. You may not feel the need to wear a bikini or designer jeans. You may think you look better a bit heavier and believe me, I look older at this low weight than I did when I had more padding on my face. To make my bum the size I want it, I have such a scrawny chest and shoulders that those shoestring tops I always wanted to wear dont look that great on me, I tend to cover and disguise THAT part of me now. So getting thin is not the be all and end all of anything either and trying to stay at a BMI of 20 for me was getting scarily into eating disorder category. It was all I thought about, obsessed about, I was pushing my body to run for hours whilst undergoing chemo, it was truly stupid. Your mental healt and ease with your lifestyle is every bit as important as what you actually weigh.