Tend to agree that it has already started and it probably gives plenty of ammunition to argue as to when the decline started in the same way as the argument as to when the second world war started. It could be the early 70's when America reached peak oil , or perhaps the crash of 2008/9 or maybe last year with the covid business.
I have my own theory but i 'll just ask if people think things have got better or worse since the early 90's.