↑Chi-Chi celebrates Gohan's birthday in Dragon Ball Z episode 171, which takes place in May, days before the Cell Games. Gohan says that the day of the celebration is not actually his birthday, and that his 11th birthday passed sometime while he was in the Room of Spirit and Time between 16 and 17 May, 767. The opening narration of Dragon Ball chapter 421 establishes Gohan's age in April, Age 774 as 16 years old (which seems to not account for his time in the Room of Spirit and Time), placing his birthday as sometime after that. Furthermore, in late November, 761, Gohan's age is given as four years old, indicating that his birthday must be some time beforethat. The timeline within Daizenshū 7 and Chōzenshū 4 suggest his birth month as just May.
↑In the original Weekly Shōnen Jump 1988 No. 46 serialization of chapter 196, Gohan states that he is three years old. The title page of the very next chapter gives his age as "four years old", and his age in chapter 196 was changed to match in the 17th tankōbon in May of the following year. With the setting already established as "five years" after Goku's reunion with Chi-Chi at the Tenka'ichi Budōkai, Gohan could not be made much older than he already was; nevertheless, he was made as old as was biologically possible, which is four. All official Japanese adaptations and publications, including the television series, follow this change.
↑"Chronological Table of DB World". Dragon Ball Chōzenshū 4: Dragon Ball Super Encyclopedia. Japan: Shueisha, 09 May 2013. ISBN 978-4-08-782499-5. (p. 17)
