In the case of the US (using the NBER business cycle dates), in the post-WWII period expansions have lasted from 12 months in the expansion ending in 1981to 120 months in the expansion ending in 2001. The current expansion is already 77 months long, longer than the previous expansion of 2001-2007.
While counting months is not a good way to forecast the timing of the next recession it is at least a reminder that there is another recession waiting for us in the not-so-distant future. And when we start counting backwards to the next recession a key questions is whether we will be ready for it. In particular, will monetary policy be back to normal and able to react to it?
Interest rates have not yet moved away from zero in either Europe, the U.S. or Japan. This is, of course, very unusual given the length of the expansion. Another way to see how unusual monetary policy and interest rates look like is to plot the difference between long-term rates and the central bank rate.