One thing we know about the Nurse's appearance is that she does not have a very attractive smile in that her smile is missing a great deal of teeth. This may be due to her older age, or it just may be due to her improper hygiene. We know her smile is missing teeth from her pun in Act 1, Scene 3, in which we first meet her. When the Nurse is asked how old Juliet is she puns that she is not yet 14 by saying that she would bet 14 of her teeth that Juliet is not yet 14, except that she does not have 14 teeth, she only has 4, as we see in the passage,
I'll lay fourteen of my teeth—
And yet, to my teen be it spoken, I have but four—
She is not fourteen. (I.iii.15-18)
Also, there are a few clues to tell us that she may be overweight; at any rate, she is certainly out of shape. If we can trust Mercutio's jesting, we may be able to say that the Nurse is both overweight and unattractive. When the Nurse ventures out to meet Romeo to learn his intentions, seeing her, Mercutio cries out, "A sail, a sail!," which can be interpreted to mean that he is seeing something interesting heading their way, like a ship (Shakespeare-navigators.com), but it can also be seen as comparing the Nurse's size to that of a ship's. When the Nurse asks her attendant, Peter, for her fan, Mercutio further jests, "Good Peter, to hide her face; for her fan's the fairer face of the two," meaning that the fan is more attractive than the Nurse is. Hence, we can also learn from these jests that the Nurse is not a very attractive person.
Even if these jests are merely an example of boys being boys, we do learn in the next scene that the Nurse is highly out of shape, which can confirm that she is obese. She complains that "bones ache!" and exclaims that she has had quite a "jaunt" (II.v.27). She further complains of being "out of breath" (31), that her "head aches," and her back aches (49-51). From all of these statements we can assume that she is definitely older, past her prime, and possibly even overweight.