The journey was supposed to take ~120 years, with about 90 years remaining, but was that supposed to be Earth time, or Ship time at half the speed of light? I'm thinking they meant Earth time, because of references to Aurora going back to Earth after ~240 years had passed. With time dilation of 15% at half the speed of light, 90 years would be about 76 years at ship time. Still longer than Jim or Aurora would likely survive, but their children should make it, if they had any. It wouldn't have to be their grand-children, by their children committing incest.

And why even have a message service back to Earth that takes a minimum of 55 years to get a reply, from where they were at the start of the movie? Which of course would take longer and longer, as they went.