Increasing the retirement age isn’t necessary. It increases overall prosperity in exactly the same way all those things that increase productivity do by allowing you to use extra labor on other problems.

Instead changing demographics means retirement benefits may need to alter their payout formulas, but more prosperity means more money for retirees in absolute terms even if they keep receiving the same percentage of GDP. IE X% of per capita GDP in 2025 is way higher than X% of per capita GDP in 1975 adjusted for inflation easily offsetting increased lifespan. The same is nearly guaranteed in another 50 years.