What are the consequences of masturbating during the daytime in Ramadan, knowing its impermissibility, and is prayer obligatory immediately after ghusl, or should one wait?

Masturbation is forbidden by Islamic law, and its prohibition becomes more severe in Ramadan. You are obligated to repent to Allah and make up the days during which you masturbated and semen was discharged, because intentionally causing the discharge of semen is one of the agreed-upon nullifiers of the fast. Age does not affect this ruling. After performing ghusl (ritual purification) from janabah (major ritual impurity), you may pray whenever you wish.