Goku’s age is unknown. Usually this question crops up because of the “Dragon Ball Z” Dragon, which occurred when Goku was 10 and it ages anything by one year to grow up with him.
However it appears that what drives this aging process is not a physical clock (or Universe) but rather self-awareness on the part of our hero – in other words, even if he had lived his entire life without knowing he was more than simply an earthling, once Vegeta abandoned him, became a king and came back from the dead as a fighter against evil then Goku would have aged naturally anyway.