You're referring to the Particle Horizon.
It is the boundary between the observable and un-observable universe.
Correct for our current level of knowledge and ability.
When we master the manipulation of time and space, can create wormholes etc, physical distance won't matter.
One or two advances in technology can bring a quantum leap of ability. The first man to fly could have met the first man to walk on the moon, they were both alive at the same time.