Andromeda we see is 2.5 million years ago so practically it is out of reach of our biological time span to last a ride to the nearest galaxy. Time bends and slows down in space but that might not be sufficient for a journey to Andromeda. What we need is a way to increase our biological life span in space.
The increased gravitational field increases the time, this is time dilation and hence we could last longer on the planets with higher gravitational force. But in vacuum when we are travelling in s a spaceship we require to minimize the age. The answer could be travelling at speeds higher than light in other dimension, say fifth dimension which makes the time to run slower and we could last longer in space.
Ageing serves no purpose in the life of a human being so it could be considered as a disease that affects the body in deteriorating organs. So to cure this disease we need a different mindset like in the bible the age of Adam is given as 930 years and if it is deemed to be possible that humans live longer then the only way to go about defeating aging is the biological treatment of the individual thus affecting his DNA. The aging is caused at cellular and molecular levels which should be treated accordingly.
Alternatively we could harness gravitational waves which appear to make us older, the less the gravity, the more there is movement of muscles hence older we get. By altering the gravitational waves of the orbiting planet or star we could infuse more life hence continue with intergalactic travel.