The Universe of Dune is set in the distant future which had a past that is somewhat similar but not really the same as ours. The first three novels which are “Dune”, “Dune Messiah” & “Children of Dune” are spread over the course of a generation beginning at 10,191 AG which means After Guild’s formation or if we convert it into our way of looking at years, it’ll be roughly in the timeframe of 22,200 AD
So, as we have explored in a previous video, there are no alien species in the dune universe, at least there are no sentient alien beings and entities, no extraterrestrial civilizations that have been encountered in the vast expanse of the interstellar Imperium. So, what do we get instead, in the span of thousands of years, we get different subspecies of humans, hybrids, clones, mutated specimens and even super beings, ones that can bend space and time to access genetic memories of the ancestors and even look into the future to the events pertaining to their descendants.
In the book, God Emperor of Dune, in Chapter 1 Leto II mentions that without Melange people in that timeline would live and die according to the ancient measure. No more than 100 years or so. which means that even though thousands of years have passed, our baseline human genetics are still relatively unchanged and the years of life are still similar but might I add, that it is slightly more in this fictional age. People in developed countries have a lifespan ranging from 70-80 years and therefore Leto mentioning that they carry on till 100 shows a 20 year increase in longevity.
However, for the majority of people, lifespans are similar to those of the 20th century. Take for example: Shaddam IV was the 81st Padishah Emperor, and the head of House Corrino that had ruled the Imperium for about 10,000. So, divide the 10K years with the number of emperors, this gives every emperor a term of about 123 years, and if we account for regents and vacant years without an active emperor then maybe we get an average lifespan for an emperor in the range of 140-150 years.
However in Heretics of Dune, as I have noted just now, here it suggests that a person with extensive access to Melange and having good genetics as well as good health care and rejuvenation tech could live in to their 300s.