However the "not how it works" comment ... well, you could make that pretty much throughout the time that humans have lived. We have been continuously changing the environment around us to suit our needs and wants. Early farmers burned down forests to get fertilized land. We domesticated crops and animals and bred them to grow the way we wanted them. We built things to make life safer, better and easier.
You could say "that's not how it works" about a tractor or wheat with multiple stems from a single seed.
But of course, there will be problems that need to be overcome if we ever do figure out ways of extending life. But again, there always have been problems with new inventions.
I firmly believe that humanity has the ability to overcome problems, develop, learn and improve. And that aligns well with wanting more life!
A group of skilled and motivated people who spend a small percentage of their lives on a ship, is going to be very different from a group that is trapped in a small town for generations.
My estimate would be that the mission to succeed is going to need 10-100x more people on generational ship compared to a transport ship. (million vs tens of thousands.)