> IIRC, it is possible to get anywhere in the observable universe in one human lifetime assuming 1g of constant acceleration.
Huh? You can’t go faster than light speed, and the observable universe is way larger than ~100 light years.
Time experienced will be slowed down for the person in spaceship as you near lightspeed
This is using the fact that at 1g acceleration, one will quickly approach the speed of light relative to its starting rest frame and time dilation will give the astronaut a _very long_ life relative to that frame.