Fourth Age

Although we have no records of the later Fourth, or any following Age, Tolkien makes a brief allusion to the future of Middle-earth in a letter written in 1958: "I imagine the gap [between the Fall of Barad-dûr and modern times] to be about 6000 years; that is we are now at the end of the Fifth Age, if the Ages were of about the same length as S[econd] A[ge] and T[hird] A[ge]. But they have, I think, quickened; and I imagine we are actually at the end of the Sixth Age, or in the Seventh."

This note is especially interesting, as it gives some ground for bringing Tolkien's dating system up to date. The fact that we are 'at the end of the Sixth Age, or in the Seventh' hints strongly that Tolkien saw some important historical event as marking the recent (or imminent) end of the Sixth Age. Each of the three Ages we know about ended with a great war and the fall of a tyrant, and Tolkien was writing just thirteen years after the end of the Second World War: could there be a connection?

While this is circumstantial at best, it does seem to hint that perhaps the Downfall of the Third Reich was to the Sixth Age what the Downfall of Barad-dûr was to the Third. If so, we can 'reset' the calendar in 1945, which would be the first year of the Seventh Age. The letter quoted above, then, would have been written in VII 14, which explains Tolkien's reference to the change of Age, while the year 2000 would be VII 56.

It's important to stress that there's absolutely no direct evidence for any of this - it's just harmless speculation. We do know, though, that Tolkien was fastidious in calculating his dating systems: it's unlikely that he would have mentioned a change of Age if he didn't have solid reasons for doing so.