It was 30 years old in the movie, 21 years old in the book it was adapted from but that didn't work in the movie.TL;DW version: (spoilers)
Everybody lines in a bubble community because they were told outside isnt liveable. But everyone is young and vibrant and there is bread and circuses. And Sex. Lots of sex. (but you dont see any in the movie)
But there is a better place where you can go to and live the rest of your life, but you have to be taken there by TPTB. (basically Heaven)
on your 27th(?) birthday you participate in a ceremony where you get chosen to go to that other place. Everybody appears to be chosen because they are never seen or heard from again. In reality they are killed. There is only enough room for so many, so everytime a baby is born they kill a 27yo.
There is also a colony of rebels that live in a run down part of the bubble. and its a lawless place that even guards are afraid to go to. They are locked and isolated in that area.
Some people are scared of the ceremony, so they try to run. There is a rumored utopia that if you get help from the rebels, they can help you escape and guide you to it You are killed if you are caught running. one guard catches on and escapes the bubble with one of the rebel women. They venture to DC which is empty and overgrown. Except for 1 man and his cats. They figure out the world ISNT toxic and everyone is being forced to live in the bubble where they are taken care of TPTB. Which turns out is a computer. (HAL's cousin?)
They go back and break in and break the computer and reveal to the rest of the colony that there is a better place outside. They wont listen until the computer melts down and the place starts falling apart and they are forced to flee to survive.
At the end they are outside and realize life as they knew it is over, and now they have to survive in the real world.
Not a great movie, but worth it on a svengoolie type program or the $5 bin at walmart.
The guy in the review I linked does a great job of explaining carousel where you go to hope to be renewed, but is bs.
Enough with the bread and circuses!
Back to your regularly scheduled doom.