There goes free child care.

People start to do all kinds of risky things shortly before that date.

Logan's Run (1976 movie) save they were expected to all die at 30, and not by dropping dead.

What would happen? Nothing good, even though it may look otherwise on the surface. There would be a lot more fascism (aka, violence) and a lot more lies (aka, not be willing to think by oneself or let anyone think by themselves). Obviously, people in power would find workarounds to exempt themselves from that (stupid) fate because, unsurprisingly, most people don't like to apply to themselves the same rules they want to apply to others, even less so rules that are supposed to kill them or reduce their hold on power. While many other people, that have no power to resist or protest said rule, would be more than happy to suddenly get access to any form of power to avoid said fate... and just like that they would demonstrate how they're exactly the same type of persons as those in power, btw.

The life insurance industry collapses overnight. So does the senior care industry. The greeting card industry also takes a hit.

People spend their last year, from 49 on, partying like Jagger.

I've seen this movie. It involves FISH! AND PLANKTON! AND SEA GREENS! AND PROTEIN FROM THE SEA!

Looks at newspaper frontpage

Celebrates

(y'all know why 😏)

People knowing when they die at the latest will probably mean more than it being 50. At some point after abt 45 life becomes either (finances allowing) a hedonistic spree, gracefully putting your affairs in order, and/or an anxious nightmare watching the hours tick by. Not sure if people will come together enough to demand a kind of pension to allow for a year or two of calm for that, but anyone that can, will take ot anyway.

People will focus on their health a little less when there's no time for many lifestyle-related illnesses to manifest.

The speed of scientific development slows. People have less time to learn, experiment, and mentor the next generation.

is it retroactive?

We'll end up sending out more expeditions

Is your question based on the 2011 movie "In time"? It gets a 6.7 but back then It found it quite enjoyable. https://m.imdb.com/title/tt1637688/

The premise different but it has the same "fixed" end date

There would be annual expeditions to try and defeat whatever is causing it.

I imagine we probably ship people off to spend their last year or so away from society so nobody has to watch their loved ones die.

Menus drop all senior citizen discounts!

Retirement age in America still gets raised.

Long term care and senior types of insurance dies over night.

Pay for your job will get adjusted so that you basically will have to work until you die. Company owners will not allow you to retire. They will find a way to screw you over.

People will care a little less about long term injuries. If the injury won’t really affect you until later in life it won’t be a cause for concern.

The massive wave of people trying to forge birth certificates saying they're already 51 and therefore exempt would overwhelm all remaining faith in official documents and government would become impossible.