It's a lucrative easy life with a shelf life. Once you're no longer of use to the Syndicate they send you back to be disposed of by yourself, "closing the loop".
Occasionally a looper won't go through with it and there is hell to pay.
When Joe's future self (Bruce Willis) is sent back he's not helpless.
No good will come of this.
CW: child murder
Why have I not seen this until now? Fuck Primer, which is overrated, this is perhaps the best semi-serious time travel movie ever. Yeah I know BTTF but that's not at all serious.
It's Terminator, "let's kill Hitler", a superhero/supervillain origin story, romance and moral fable all in one and at no point does the time travel aspect get used for "hey look how smart and twisty we can be". Which always irritates me.
Rian Johnson doesn't mess around with any kind of immutability of the timeline: things in the now directly influence the future and this is used to gruesome effect. Memories get messed up but old Joe can remember some of what young Joe did or was about to happen so at times is sort of prescient but is also constantly changing things. Causality is maybe fucked: there's a reason only criminals time travel.
It does slow a bit once present Joe ends up at the farm with Sara (Emily Blunt) while old Joe causes mayhem in the city but it's gripping throughout. Both Gordon-Levitt and Willis are great with it not being really clear which one is really the bad guy. They sort of both are and aren't.
Highly recommended 9/10 up there with things like The Prestige for being proper sci-fi that also works as straight entertainment without compromising either aspect of the whole.