Rent Jack (1996)

Just like any kid, ten-year-old Jack wants to go to school and play with others his own age. But Jack (Robin Williams) is no ordinary kid. A rare medical condition has caused Jack to age at four times the normal rate, making him a child in a man's body. On Jack's first day at school, he fits neither into the desk nor in with his classmates... who at first consider him more of a freak than a friend. It's not until Jack's awkward encounter with girls and his calamitous tree-house sleepover that the 5th grade becomes the adventure of his life.