Goku is introduced in the Dragon Ball manga and anime at approximately 11 or 12 years of age (initially, he claims to be 14, but it is later clarified during the Tournament Saga that this is because Goku had trouble counting), as a young boy living in obscurity on Mount Paozu.
Who cut off Goku’s tail?
Goku loses his tail three times: the first time was when Puar transformed into a pair of scissors, and cuts it off after Goku transformed into a Great Ape in Pilaf’s Castle. It ends up growing back during his fight with Giran at the 21st World Martial Arts Tournament.