As for the "You can weigh whatever you used to," that just says you know very little about human development. Bodies tend to have hard minimums they don't like to go below. For most people, this raises slightly as they age. I'm not saying you can't go below it if you starve yourself or something, but it is not healthy and cannot be done easily.
Bollocks, spoken like someone who is overweight (which you claimed you were). I've learned a lot about the human body in the last few years as I've stopped making excuses for my weight and started doing something about it. I hardly starve, quite the contrary, I'm on a 3000 calorie/day diet and it barely lets me keep my 22 BMI (if I go under that for a few days, I quickly shed weight with my training regiment). I don't do protein powders and other gym type supplements because my goal is not to look like body builder.
Again, stop looking for material on the web that tells you you're not being lazy but that it is normal to not be fit in your 30s. It's all plain false. You can weight 185 now just like you did at 18, especially if you're 6'1", which is nothing spectacular, without starving yourself at all.
As for BMI being stupid, thank you for ignoring all my points about it. It is an acceptable measure for the average person. It does not apply to some individuals, of which body builders are a part of (football players and other atheletes also using body building techniques would fit under this "does not apply to" rule).
Anyway, I seriously doubt anyone would mistake a body builder/athlete for an obese person, so the point is moot. If someone has a BMI of over 35 and is obese, not muscled, you won't actually need the BMI test to tell you he's fat. If you think you do, you're probably fat yourself.