Well the common trope used in a lot of scifi movies and TV shows. Hypersleep which comes in various ways to show how you can make 100 year journeys and still be the same age.

After watching several movies with the same, or similar idea it just dawned on me that that possibly the only way this would work is that they deliberately kill you when the ship is launched and the machines keep your body preserved in some fashion till you reach your destination where you are somehow revived and brought back to life.

Of course that would not explain stories where your body is kept alive with beating heart and such, but I just think that if it were possible to do that this is the only likely way they would do it.

Can we discuss this idea more?