Must one make up for missed fasts and prayers after repenting from masturbation, given that one was ignorant of its prohibition?

Ghusl (ritual bath) is not obligatory for someone who masturbated unless semen is discharged. You are not required to make up the days in Ramadan when you committed this act, even if it resulted in the discharge of semen, as long as you were unaware of its prohibition. As for the prayers you performed without ghusl, the majority of scholars hold that they must be made up, and it is safer to make them up.