If you can somehow make a ship capable of constant acceleration at 1G, and had enough shielding on it to protect it against the radiation, you can travel to any point in the observable universe, in a human lifetime.

If you just keep accelerating and left as a 20 year old, you'd be in your 50s when you saw the final stars born and die in 100 trillion (earth) years time.

That's how crazy relativity and torchships are