The average lifespan of a polder is almost impossible to calculate. Most polders live for around the same amount of time as a human, but more frequently than one expects, a polder will exceed that period. Quite a few will live almost as long as the oldest dwarves, pushing into their fourth, potentially even a fifth, century.
Academics have a number of theories as to why these variable lifespans may occur. One theory is that the more that the polder taps into their trickster magic, they are sacrificing the duration of their life. While others theories is that the two different lifespans are holdovers from when polders were once two different ancestries. These two intermingled, and centuries, or even millenia, later, the only sign of this is the occasional extended lifespan.