While Saiyans have a human life span, Saiyans age different, they have long childhoods and stay on their prime until their 70s-80s (their hair does age, it gets white), after that they grow frail very quickly. So Goku will probably not face that issue. Also there was a MMO which AT wrote the scenario, the MMO is set on the future, but the coolest thing of that MMO is the fate of Goku and Vegeta: basically once they sensed they where about to reach the point on their life when they would start growing frail, they just went to have a fight to the death to die as warriors, they just went away and a day latter a clash of energy so strong happened that it create a galaxy on the edge of the known universe, they basically went out in a blaze of glory,