The theme of Katherine Mansfield's "An Ideal Family" is that of the problems of growing old. 

Mr. Neave sits in his chair at his office and reflects that his son Harold does not take his position seriously as he has not returned to the office from lunch until after four o'clock. His daughters spend their days engaged in their hobbies and social life; in fact, his girls encourage him to find hobbies that interest him enough that he will stay home and not go to the office. 

Old Mr. Neave, forgotten, sank into the broad lap of his chair....There was no doubt about it, he was tired out; he had lost his hold. Even Charlotte and the girls were too much for him to-night. They were too ... too ... But all his drowsing brain could think of was - too rich for him. 

Mr. Neave perceives himself as alienated now from his family and their rich modern life and ways. "Who was he?" he ponders. He feels that his family are strangers, he is forgotten, and life has "passed him by." The world that Mr. Neave has known is gone; even his wife does not seem to him to be his. Mr. Neave begins his passage to death as he grows weary of a life from which he feels alienated.

Katherine Mansfield excels at revealing the inner thoughts of her protagonists, and their limitations and struggles. This story is no exception. In "An Ideal Family," we are shown the thoughts of old Mr. Neave, who, in spite of his obvious financial and social success in life, is now struggling against inevitable old age and feeling left behind and ignored by his family. One repeated symbol that appears in this tale is that of an old withered man:

And somewhere at the back of everything he was watching a little withered ancient man climbing up endless flights of stairs. Who was he?

This is a symbol that occurs again and again when Mr. Neave is feeling tired of life and forgotten by his wife and children. Clearly, therefore, one of the principal themes of this story is age and how we accept it, and how often this is a massive struggle, as symbolised by Mr. Neave's stubborn refusal to give over his business to his son and his insistence to walk to and from work.