During Goku’s time in the afterworld, it seems that his physical body doesn’t age pausing his biological block. Goku has made several trips to the otherworld, both choosing to stay to train with King Kai. This is because, in the Dragon Ball universe, it’s possible for a possible to die, but for a spirit to exist in the other world.
While we have explained how old Goku’s Chronological age is, his physical age is different. Some people think Goku is younger in Dragon Ball GT as he has the appearance of a child however, this is only because at the beginning of the series Emperor Pilaf wishes Goku to be young again using the Black Star Dragon Balls.
However, Dragon Ball GT is not canon and is not part of the main storyline. Goku is 42 years old in Dragon Ball GT as it takes place age 789. It’s a shame that these movies are no longer officially canon as they were both fantastic, and it seemed like a bit of waste retelling the same story. This means that Goku is still 41 years old during the movie as it was set in Age 778. The Battle of Gods takes place at the same time as Dragon Ball Super, as Dragon Ball Super retold the same story. With hints of Dragon Ball Super 2 coming out in 2021 then we expect Goku to get even older as no one mortal or God seems capable of killing him. The final Tournament of Power takes place in the Age 780, meaning that Goku is now 43 years old in the anime right now. This was a very special age for Goku as he tasted God Ki for the first time and was set on a path to getting SSB and eventually Ultra Instinct. Goku is 41 years old at the start of Dragon Ball Super in Age 778. The end of Dragon Ball Z is marked by the death of Majin Buu, and this happens Age 774 making Goku 37 years old. Goku is 24 years old at the start of Dragon Ball Z when his brother arrives and kidnaps poor young defenceless Gohan. This would make Goku 19 years old when he defeats Piccolo Jr at the end of the original Dragon Ball anime series. Dragon Ball took place over a seven-year period ending Age 756. Goku is 12 years old in Dragon Ball when he first meets Bulma in Age 749.