Anyone know what the maximum number of years of life rejuvenat can add? I remember seeing Inquisitors five centuries old in some of the novels. But I wondered what the upward limit was... 1000? 2000? What's old age for a rejuvenat candidate?

the most ive heard is 300 to 500 years

As far as I know, 500 years is tops. Eventually, the body will give way no matter what. The only ones who can reasonably grow older are Space Marines because they do not age like normal humans - they happen to always die a violent death, however.

I don't know of any concrete upper limit.
And unlike the other posters, I believe that the treatments can effectively halt the aging of the body, thus making your theoretical lifespan unlimited. There would, however, be practical limits.

As your body receives these treatments it builds up a resistance to them. While this won't make much of a difference over one or two centuries, beyond that the treatments need to occur more and more frequently to keep you in this unnatural state. Those above the age of 500 would surely need treatments every decade or even year to avoid aging.

More debilitating, however, is ones mental processes. Just like real people who've reached the age of 80 or 90 without any serious health problems start to be less coherent and out of touch with surrounding society, so would people relying on these treatments find their minds breaking as they have to process more memories and experiences than it's supposed to have to deal with in a lifetime. Memory lapses, neuroses, psychoses and general mental instability becomes more pronounced as time goes by.

Of course, that's just the way I see it.

Harboe said:

That doesn't quite work, that means people with very full lives are going to have their faculties break down faster than those without and that is actually contrary to the findings. People who live active, challenging lives retain their mental faculties much longer than those who live in isolation with little to stimulate them mentally.

Additionally, with the potential for implants that could deal with any - however unlikely - mental overbleed, this seems live an even less relevant issue.

For the sake of setting flavor I would say no more than 500 years simply because having humans live eons would detract from the grimdark essence of the galaxy ... this does not stop you, however, from allowing a certain villainous npc from finding a way to extend his life beyond accepted limitations, if that works for your story.

Rejuvenat treatments don't seem to be perfect. You need to keep taking them. This indicates that they produce temporary modifications.

In my article on age and experience:

www.darkreign40k.com/downloads/dark-reign-supplements/age-and-experience-color-/details-3.html

I have a section on old age and Rejuvenat treatments. These are interconnected in terms of rules but basically the treatments range in quality from poor to best and reduce the physical age of the recipient so that the negative affects of aging are staved off for longer periods of time. However the maximum number of rejuvenat treatments avaiable is equal to the TB of the character. Once you've had that many you cannot take anymore.

Hellebore

This would likely massively depend on the kind and quality of your treatments. A High Lord could conceivably have access to much better versions of the treatments that keep a minor noble alive for perhaps two centuries.

Just a little bit of background, I am a medical immunological reasercher, a part of my field looks at anti-agaphic reagents, essentially longevitiy research. Given the technology in 40k, the augmetics available, the ability to fix genetic dmg (apparently you can heal radiation dmg and the tech preists have chambers that can regenerate important people) realistically there is no upper limit, the body only gives due to genetic dmg and physical stress, if you can repair that then you pretty much live forever, pls remember the game has rules for augmetics which reapir massive dmg in real time (like the augmetic you can purchase in the inquistiors handk book which regenerates wounds per a combat round) as such if you can get access to the tech (which really would be avaialbe to any tech priest or member of the medicae divsion) there is no real limit to age.

HOWEVER, thematically in the game they dont really address this and this is really a massive failing of many many Sci Fi settings failing to take into account the real effect technology would have on human medicine and society in general, I would guess that there is a upper limit given people do die of old age in the setting but from my point of view physically you can easily live forever, the big issue is mental ennui that would build as you start to get REALLY old (like 1000s of years old). If you are interested a game called Eclipse Phase by catalyst games really address's the way technology effects society really really well and overall is a great game.

In my games pretty anyone who his privelage or access to medical technology can live forever and never die of old age. However exotic diseases, misadventure, noble intrigue and so on will catch up with you.