Stanley Burnell is of course the main middle-aged character in these two stories, and he is one of the main characters that the shifting authorial focus zooms in on periodically. It is thus this character that Mansfield uses to explore her presentation of middle-aged men.
It is interesting that although Stanley is shown to be the "master" of the house, and that all the women manage the move to the new house in "Prelude" whilst trying to satisfy Stanley's desires, there is always the sense that he is a subservient character to the dominant female figures in the household. Note how in "At the Bay," he is even shown to be a figure that is not wanted, as the women are relived when he goes to work: "There was no man to disturb them." Whilst Stanley gives every appearance of being the master of the household, it is obvious that his character is limited compared to those of the women and he is clearly ruled by them and in particular his wife and her moods. Note how his imaginings are limited to what he would do at the weekend:
He began to plan what he would do with his Saturday afternoons and his Sundays. he wouldn't go to the club for lunch on Saturday. No, cut away from the office as soon as possible and get them to give him a couple of slices of cold meat and half a lettuce when he got home. And then he'd get a few chaps out from town to play tennis in the afternoon. Not too many--three at most. Beryl was a good player too...
Note how trivial his thoughts are. He is presented as a man who is curiously limited in terms of emotion and deep thinking compared to the internal monologues of the women that we are persented with. We can see this again when Stanley Burnell dreams of singing in the church but obviously is more focused on what others may think of him and his own self-importance than any genuine religious response.