In the short story, Reginald on the Academy, Saki writes:
“To have reached thirty,” said Reginald, “is to have failed in life.”
Why does Reginald consider it a failure to reach the age of thirty?
It is simply an ironic summary of the preceding sentence:
“Someone who Must Not be Contradicted said that a man must be a success by the time he’s thirty, or never.”
If you have achieved nothing of note by the time that you have attained your thirtieth year, you are unlikely to achieve anything afterwards.
In the first story in the Reginald collection, "Reginald," he teases an Anglo-Indian soldier for referring to the year 1876. The narrator comments, "Reginald ... never admits to being more than twenty-two." So, like some women, Reginald not only values his own youth but refuses to admit that he is actually aging. He is not someone who will ever be a success but he will also always be, in his own mind at least, young.