Well according to the file on the facility, the machine only has enough power/materials to last about 5000 years from initial construction. And Lolimura later says that they're on loop number high 400's, so they're actually running pretty close to the operational limit and run the risk of the entire facility failing if they don't make it out. It's why they need to do it now, rather than loop again like Ida wants. It's less Sector 0 being reset and more the whole facility being deemed a failure by Universal Control and scrapped.
Hmm, I just went and looked it up and the timelines for each zone are intened to run from, for example in Sector 1, 2089-2109. She does say that when they reach adulthood they get pulled out for training so maybe it's just an early thing.
The fact that they should have been released at adulthood, but when they pop out they're the current age, makes me think that the bodies are grown from scratch every loop and probably broken down for parts once the cycle fails (because if they kept the old bodies then all the loopers would easily get out and not have to wait for them to make new bodies for them).
One thing I really enjoy about the ending is how they go both for and against the idea of fate. Some events repeat themselves down throughout time, but other times the same characters go a wild different way. Like Juro and Morimura are together in 2188, then again in three loops before, but come current loop and Juro falls for Megumi when they meet.
Also how once you hit the end you can view the timelines of every MC no matter how little they appear, like Tamao, or Juro two loops ago, or 2188 Megumi.