I think it's worth playing this out a bit, because I'd claim there's an exponential curve here. Offer someone 500m (hell, even 1m for many) for one year, and I

I think it's worth playing this out a bit, because I'd claim there's an exponential curve here. Offer someone 500m (hell, even 1m for many) for one year, and I doubt you'd find many who would say no. There's a margin at which you would be losing so much life experience that you wonder what you even live for (20y), while shorter periods (1, 2, 5, even 10y) aren't so defined. Also, I read this as you lose 20y from the point of the deal (eg. 20yold coming back as a 40yold) rather than taking years off the end of your life, which I suspect is a more palatable interpretation for most.