Now we all know this is not STATED.....but Goku did take the life of a KAI.....KAI's live for a thousand years. Does that mean that Goku can live longer, since he's a saiyan that makes him age EVEN SLOWER. Not die due to age. Goku has the life force of a Kai within him....meaning that Goku, who's BODY was around 27 or 28 years old at the time can live on and stay young. Not sure about Goku's age.