See that this would probably have quite a lot of social side effects:
- As someone pointed, an older people society (even if they appear younger) is likely to become more conservative, probably leading to stagnance
- If people don't get Elder and die, unless there's some way to avoid procreation, population wil lgrow out of control and scarcity of ressourdes
- If people does not see life a something ephimeral, they are unlikely to risk their lives. So you will have less people wanting to work in high risk Jobs (as military, firemen, etc).
- Sure there are more of them, some of them I cannot think about right now, and others that can only be discussed in the Pit...
The combination of points 2 and 3 above gives us an interesting situation, where the resources are scarce (probably leading to fight for them) while people do not want to risk their lives (so limiting this same fighting).
With advancing technology, particularly maker technology and robotics/automation, isn't there the possibility of some parts of the 3I becoming post-scarcity societies within the wider Imperium? Utopian wonderlands where people can live as long as they want?
But if people can have whatever they need, and live as long as they chose, then the thing of value would still be that which they simply cannot have.
If honour, service and duty are cherished concepts at the heart of Imperial culture drawn from the dawn of the 3I (don't throw things at me for mentioning this again...) then the honours that come from military service could be of value as they couldn't be purchased. Backing up a personality could provide a bit of a safety net, but the sort of person who would throw away their life for glory wouldn't be the sort of individual a military organisation would see to include in it's ranks.
People could still chose to work, as it provides meaning.
Long life doesn't have to mean immortality. It doesn't have to mean uncontrollable population growth (hands up if you've had enough kids for more than one lifetime), but there's no doubt it would bring plenty of social and cultural dilemmas to crack.