The age at which we do our greatest work
John J. Reilly was born in 1954. He wrote Spengler's Future in 1992, and published it in 1993. He was thus 38 or 39 when he started to produce his characteristic works.
John continued to write up until his death at the age of 58, a writing career of two decades. In that time, he published four books and hundreds of book reviews and essays, along with his blog The Long View.
Spengler's Future was not the future that John actually expected to happen, but he wanted to explore what it would mean if it did:
As a matter of fact, these invented events do not closely resemble the future which the author himself anticipates. That future has far more in common with the ideas of Teilhard de Chardin (or at least Teilhard in his more Augustinian moments) than with those of Oswald Spengler. This book, indeed, can be taken as an attempt to exorcise a private nightmare. At least in the author's mind, this is what will happen if Teilhard and similar optimists turn out to be wrong. Despite its fantastic elements, you will be looking at a "realist" version of the future, the one we will get if the future is like the past.