I've never seen it adjusted for any of those things and I can assure you that the children's one is a load of old bollocks. DS' BMI at beginning of Year 6 when they did the formal measurements came back as he was significantly too high. I was shocked - because in fact, he had been quite overweight and we'd all spent a lot of time and effort and he was looking great.
So I went and had a look at the calculator myself. DS is on the 91st percentile for height. When I put his height and weight into the calculator with his actual age of 10, it said his BMI was too high. When I shifted his date of birth, but left height and weight the same, it said he was perfect.
Then in small print, I saw that they openly admit that the results are faulty for children who are extra tall or extra short. But in the meantime, I'd received the dreaded, "your child is overweight, you are a terrible parent" letter.
As for adults, there are lots of variables that aren't taken into account. I have very thin, very light bones. The truth is that whatever my BMI is, in reality, I'm actually WAY fatter because the vast bulk of my weight is coming from fat, not my frame. DH is the exact opposite - his BMI shows up as being not great, even though when he is measured on those fat machine things, he has something ridiculous like just 7% body fat!