What is the ruling concerning a young man, 13 years of age—the age of puberty—who did not fast half of the month of Ramadan, despite his ability to fast, because his family believed he was unable to fast due to health issues?

Fasting is not obligatory until after puberty, so there is no sin upon one who neglects it before then. After puberty, it is obligatory to make up the days missed from Ramadan, even if the breaking of the fast was due to a mistaken belief in one's inability to fast, as the Prophet, peace and blessings be upon him, said: "Indeed, Allah has pardoned for my Ummah their mistakes, their forgetfulness, and what they are forced to do."