It used to be most NHS spending is done in last 18 months of life - I think that holds true for whatever age the death occurs.
https://www.nuffieldtrust.org.uk/news-item/over-80-of-healthcare-cost-in-the-final-year-of-life-spent-on-hospitals
The figures reveal that the UK public purse spends five times the amount supporting people in the final year of life as hospital inpatients than it does supporting them with primary, community health and hospice care
That is a big thing the government is apparently looking at - if we can avoid hospital admissions and provide more other cheaper care. Certainly most people don't want to be in hospitals and most don't want to die in them yet despite that most do at the minute.
There are fears euthanasia could take away resources from end of life care - but I think that will depend on the implementation.
One thing that will likely happen is longer working ages - so there legistalation that means state pensions age can be raised till it hits 70. I suspect we'll see more of the USA model - retriement but p/t flex work during it in early years. I know DH uncle doing driving deliveries in his retriement - he's 70+ but still taking on some shifts (and providing childcare for GC). This doesn't tend to go over well on MN when mentioned though. Also impacts family help for child care.
Japan done well with it's aging population but it has led to high government debt - they manage as a lot held by it's own citizens. It could be a contibuting reason behind our increasing debt as well.
One big problem is once you hit an increase in older dependents it's actually hard to add kids - as they are dependents for decades - so they'd just add to government and families burdens - you'd get a U curve so added pressure on working population both ends. Immigration helps mitigate that - tends to be working age people but they age and stay and it adds pressure onto services and resources such as housing - making competion in working population even higher and decreasing fertlity levels - as well as more cultural problems.
There are no good solutions out there so we'll just have to manage the population decline.
We've raised retiment ages - added more mothers to working population - push more onto individuals - with long NHS wait lists, more private care and pensions. We're in a much better position than countries that haven't raise retirment ages as quickly.