The ever suspicious Arralen.
I don't know the numbers either. JK might well be keeping it secret for me as well as for you, but it is probably out of lazieness and a feeling that it matters little anyway
I think death gives 30% per lvl of not getting diseased during winter age. Not sure of exact numbers. It might be 20 or 40. Thus death mages rarely die from old age.
The ageing chance is proportional (IIRC) to the max age of a unit, so an Oracle of the Deep is much less likely to get afflictions than a short lived Bandar Commander. Also the old age penalties are dependent on lifespan.
Nature adds max age as do earth magic for inanimates IIRC.
Undead have generally long life spans, but can get old age. However, they are still undead and do not suffer from disease. Only the reduced stats from bodies becoming more brittle and unrealible. Hmm, soulless should have very short lifespans, or transform into longdead. Might have been discussions on this topic earlier in the beta or in elsewhere, I don't remember.
The effect of the growth scale was mentioned in the beta, but I'm not sure if numbers were presented. I think it was.