Regarding Europe, I'm really only nostalgic for periods before 1914, though in those countries that kept their monarchies, subsequent decades can be considered preferable to the present in some ways. But regarding parts of Asia and Africa, I'm quite fond of the moderate Muslim monarchies of the mid-20th-century (particularly those of Iraq, Afghanistan, and Iran) and the last Christian Empire of Ethiopia, which takes us into the 1970s. So how long it's been since things were sort of acceptable depends on what part of the world I'm thinking about. It would have been interesting to have been alive at the time of the Shah's 1971 Persepolis celebrations, if only to follow the coverage from afar--and then horrify leftists by defending the Shah throughout the 1970s. There are no really controversial monarchical regimes today I'm interested in defending.
The Western Hemisphere, it seems, has been largely a lost cause from a monarchist point of view for a long time, certainly since Brazil fell in 1889, Canada and the Caribbean excepted.
Of course, ideally monarchism should not be primarily about nostalgia: if more monarchies had endured into the present, if one could visit the official websites of the current Shah of Iran or Emperor of Ethiopia or King of Hungary or Tsar of Russia or King of France, there would be no need for us to be as fixated on the past. I want Monarchy to belong to the future as well, but sadly the world does not seem to be listening.