I think modern lifestyle, mixed with sedentary teens, overweight obese diabetics will lead to a reduction in the eventual life expectancy, coupled with an increasing retirement age of 70 for that group will solve much of this issue itself.
Tbh the system was never designed for the majority to not only reach retirement age but live a good fair few years after. A good citizen should pay tax all their working life and then die quite soon after they start to draw their state pension, an even better citizen will die before and leave no will or dependants.
I can see the state pension being means tested in the future though which will impact the middle ground the hardest, those that have saved but need the state top off to be comfortable.