Since when does adults even think of the looks of a 16 year old.
I'm not exactly sure where you're going with this. I think you can tell if someone has the means to make it as a model, without fancying them.
If Brooklyn didn't have famous parents, I don't think he'd stand a chance otherwise, whereas Gabriel (?) Day Lewis has very 'model' type looks.
Besides which, BB has been shoved into the public eye. People are going to comment on what he looks like, whether we like it or not (which is not to say I agree with it).
There was a similar thing happened with Jerry Hall and Mick Jagger daughter. These days it tends to be not what you know, but who you know.