Must a vow made at the age of seventeen to pray all missed prayers from before puberty be fulfilled, knowing that prayer was not obligatory for me during that period?

If you made a vow to make up for missed prayers from before puberty upon achieving a high grade in your studies, this is a valid vow of obedience. You are obligated to fulfill it, based on the Prophet's (peace be upon him) saying: "Whoever vows to obey Allah, let him obey Him." If this becomes difficult for you, then an expiation for breaking an oath will suffice, according to the Hadith of Ibn Abbas: "Whoever makes a vow that he cannot fulfill, its expiation is the expiation for an oath." The expiation for an oath is feeding ten needy persons, or clothing them, or fasting three days for those who cannot afford that.