If you had a magic rocket with unlimited fuel, and if your body could withstand any acceleration, then there would be no lower bound to how quickly you could get from one place to another in your own in your own subjectiveproper time. You could travel from here to another galaxy and back in a matter of minutes, but...
...if you sent a powerful radio message to that galaxy before you took off, you would never be able to catch up to it, and...
...when you returned, you would find that millions of years had passed on Earth while you were away.