According to the code, Elders' minimum age is 2.428 multiplied for the constant k[lifespan]SimDaysPerAgingYear, which is 2 for Short, 4 for Medium, 7 for Normal, 15 for Long, 75 for Epic.
This means the minimum age in days for Elders should be:
- 4.856 for Short lifespan (25 days total)
- 9.712 for Medium lifespan (50 days total)
- 16.996 for Normal lifespan (90 days total)
- 36.42 for Long lifespan (190 days total)
- 182.1 for Epic lifespan (970 days total)
After this minimum, each day there's a probability the elder will die, as follows:
- 30% for Short lifespan
- 20% for Medium lifespan
- 14% for Normal lifespan
- 6% for Long lifespan
- 3% for Epic lifespan
The only modifier I found is for elder marathon runners (max athletic?), which have their daily chance of dying multiplied for 0.75 - for example 10.5% instead of 14% in case of Normal lifespan.
Unless there's something else hardcoded elsewhere, this seems to be the only thing that affects lifespan.
BTW I foresee Elders' persistence in case of Epic lifespan truly terrifying.