Must I make up two years of prayers and two Ramadans of fasting due to practicing masturbation in my youth and being unaware of the obligation to perform ghusl from it or that it invalidates fasting, especially since I am not certain if semen was discharged?

Masturbation (self-abuse) is Islamically forbidden, and it is obligatory to abandon it and sincerely repent for it. There is no sin upon you for what you did of it before puberty or when in doubt about it, because the Prophet, peace and blessings be upon him, said: "The pen has been lifted from three: from the sleeper until he awakens, from the afflicted until he recovers, and from the child until he grows up." Similarly, for what you did of it after puberty out of ignorance, based on the Almighty's saying: "And there is no blame upon you for that in which you have erred, but [only for] what your hearts intended," and His saying: "Our Lord, do not impose blame upon us if we forget or make a mistake." If you are not certain that semen was discharged, then there is no make-up required for you in fasting or prayer, because doubt concerning the discharge of semen does not necessitate a ruling.