Female breasts are not fully developed until the first pregnancy, usually enlarging their size. Thus the tendency towards bigger breasts could also be attributed towards women who have already 'proven' their fertility. No surprise then that most of the prehistoric fertility goddesses are pictured as big-breasted and round shaped. Various treatments, including silicone implants, have been also invented with the sole purpose of enlargement. And breast removing surgery, despite being non-life threatening, is often causing great psychological trauma due to loosing this so important indicator of one's sexuality.
Face is one of the body parts people pay most attention to.
Because even in the case of non-verbal communication so much can be read from face only. The preference for younger women is quite strong, maybe because they exhibit many of the other desired features. Though many admit that younger girls are boring in the longer run due to immaturity, many a man find them irresistibly attractive, at least at 'the first sight'. This preference for purely biological features over those 'socially acquainted', such as maturity, education, emotional stability, material position etc. First they do not exclude their age - this is one of the 'taboos' of our times.