Is it obligatory to re-perform past prayers for someone who was unaware of the obligation of ritual bathing (ghusl) after major ritual impurity (janabah) for ten years due to practicing masturbation?

If you performed ghusl (ritual bath) from janabah (state of ritual impurity) by pouring water over your entire body with the intention of removing the ritual impurity or performing prayer, then your ghusl is valid and your prayer is valid. As for the prayers you performed without tahara (ritual purity), they are a debt upon you that must be made up according to the majority of scholars, to the best of your ability, provided it does not harm your body or livelihood. Know that masturbation is forbidden, and repentance from it is obligatory.