firstly - they are fair game - but when the model posts it up, but commenting on the things that the photographer cannot control, i.e. looks (at least to a certain extent, bar plastic surgery, which i think you agree is drastic) is at best akin to me posting up a picture that you had taken and letting people comment on it. this is a photographic forums, if you want comments on your model's looks and not photography, post up the pictures on hwz.
obviously when it is a male there will be less countercomments. i think it is only fair to say that age is not such a sensitive issue with males. as to whether this should be the case, that is not the point here. if it is indeed the photographer's fault that the model look auntie, i.e. he didn't correct inappropriate styling, he shot her from a very unflattering angle, then say it is the photographer's fault. this is a photographer asking for critique here, he did not come here to show off how pretty his model is. i'm sure you of all people would agree that whether a model is auntie or not in reality, while extremely subjective, has nothing to do with photography.
well, if the ballerina is clearly not fat, but the photographer makes her look fat, then you are more than free to comment on it. if the ballerina is fat, and the photographer presents reality, then say "fat", got what use? that's a waste of your calories and time in typing out something that we all already know. why not just add in that "this is a picture of a ballerina and it is a fat ballerina at that."?