From the front as well as from behind - well, absolutely flat woman. Only one advantage is obvious - well-designed orifices. And of course due to the flat buttocks it's very convenient to pull your partner in the anus, even without bending her over. And I don't see anything else interesting in this lady! The man is basically of age, so probably the determining parameter for him is the age of the woman and the possibility to work her anally!
I have repeatedly advocated this kind of close family ties. It is better to have granddaughter at home, and grandfather to have some fun and share the experience, than to go back and forth with someone I do not know.