The age at which Monkey D. Luffy, the adopted brother of Portgas D. Ace, consumed the Gomu Gomu no Mi Devil Fruit in the One Piece manga has been a topic of discussion among fans. This rare fruit grants extraordinary powers to its consumer but, at the same time, deprives them of the ability to swim, a disadvantage in the sea-based world of the One Piece universe. Luffy was still a child when he ate the fruit, granting him the ability to stretch his body like rubber.
While there is no confirmed age for when Luffy consumed the fruit, some clues indicate that he was likely around seven years old. Firstly, a flashback showing Luffy consuming the fruit in his childhood portrays him as around that age. Secondly, the first chapter of the One Piece manga introduces Luffy as a seventeen-year-old pirate, suggesting that ten years have passed since he ate the fruit.
Thirdly, the creator of One Piece, Eiichiro Oda, has mentioned in an SBS question and answer session that Luffy was “around ten years old” when he embarked on his pirate journey. This statement is consistent with Luffy consuming the fruit at around the age of seven. Finally, the title of episode 4 of the One Piece anime, which features the flashback of Luffy consuming the fruit, hints at Luffy being around seven years old at the time.
In conclusion, while there is no definitive answer regarding the age at which Luffy consumed the Gomu Gomu no Mi Devil Fruit, it appears likely that he was around seven years old. The consumption of this fruit set Luffy on the path to becoming one of the most formidable and infamous pirates in the One Piece universe, despite the disadvantage of being unable to swim.