What are the motifs in A Mathematician's Apology by G. H. Hardy?

Ageing and depression is a recurring idea in the narrative. A Mathematician's Apology was written during the final years of Hardy's life, shortly after a heart attack and a series of other physical ailments had rendered him mostly sedentary. This theme colors much of the text. Whereas in his prime he could devote his days to intense studies of concepts and vigorous games of cricket, those abilities were long lost to him as he was writing this memoir.