Fair points. I'm don't think what we understand about longevity is as bad as what we understand about investments.

I suppose what I'm looking for is a model which 1) doesn't have any obvious bugs, 2) doesn't contradict anything we do know, and 3) has at least some evidence behind the model. If it produces a fairly wide distribution because that represents the (poor) state of our knowledge, I think that's fine.

The issue of correlation vs. causation also is important, and I'm not sure what we could do about it short of allowing someone to turn off certain features of the model if they believe them to be untrustworthy. For example, I've seen a fair bit about how marriage is correlated with an increase in longevity, and it seems obvious to me that any similar sort of social structure where one has frequent socialization and possibly receives feedback and care is probably where the real benefit is. So I think you can say you are married if you believe your situation is equivalent in some way. Obviously these details need to be shown more rigorously, but this is the basic argument.