The original Old Age Pension introduced in 1908 only paid out to those aged 70 or over (and you had to be 'of good character' !). And I think that was when life expectancy was only a little bit higher than that.
Now people are getting paid State Pension for decades and it's simply not sustainable.
Going forward I think there are three options to make the cost of State Pensions affordable - either increase the age at which you start paying it, decrease the amount (by abolishing the triple lock and letting it deflate away) or means testing it.
There is a difference between retiring and receiving state pension - I'm retired and have been for a number of years, am just about to start receiving a work pension but won't get my state pension for a couple of years yet. If people want to stop working before they reach State Pension Age then they need to plan how they will manage to fill in the gap, probably by using savings and/or drawing down other private pensions.