in Majora's Mask. Young Link is advantageous over his adult form in that he can access certain small pass ages and crawl spaces, as well as the ability to equip and utilize key items unusable by Adult Link. Despite this, Young Link lacks the fighting power of his later self, as well as access to Adult Link's equipment. Young Link is also an unlockable character in Super Smash Bros. Melee. He does not gain weight in any of the games he is in.
Young Link does not speak at all in the games (except for grunts and screams), meaning that he may not be very expressive. However, this may tie into the theory that Link's actions are to reflect that of the player. He rarely eats in the games (only potions and milk), suggesting hylians can go long periods of time without nutrition or Link's appetite was not put in the gameplay to prevent added difficulty.
In the manga version of Ocarina of Time, Link was often hungry during the start of his journey. This was shown when he hitched a ride on a milk cart and (despite having already a drink of the cart's milk) began eating the food that was sold in the market, however, he did not have enough money to pay for the food.
Weight GainYoung Link has not gained weight in either the games or manga. However, Deviant Art user, prisonsuit-rabbitman posted a drawing showing Young Link and Sora (from the Kingdom Hearts series) trying to see who could break their belt first by eating until their bellies were too big for their belts. Young Link managed to break his belt first. The image can be seen here: http://prisonsuit-rabbitman.deviantart.com/gallery/?q=link#/d2s4cob