All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
There is no doubt that Riba is one of the greatest prohibitions. It is one of the seven destructive matters; the person who consumes it, the one who gives it to others to consume, and the one who helps them are all cursed.
Jaabir narrated that the Prophet said “Allah has cursed the one who consumes Riba (i.e. usury or interest), the one who gives it to others, the one who records it and the one who witnesses it (its transaction).” He added: “All of them are equal in sin.” [Muslim]
Therefore, it is not permissible to be involved in Riba unless the dire necessity is confirmed; a necessity that permits committing what is forbidden, namely when a person reaches a point that if he does not consume what is forbidden, he will die or will nearly die.
The devil incites the person to be involved in Riba and whispers to him that there is no way to fulfill his needs without getting involved in it. However, if a person seeks what is lawful, he will surely find it, and whoever fears Allah, Allah will facilitate his affairs and will provide for him from sources he never expects.
Hence, seek Allah’s forgiveness for what you have done; whoever repents, Allah will accept his repentance. Now, you are obliged to repay the original loan only without the interest. You do not have to pay the interest if you can avoid it.
Young age does not exempt one from sin unless the person has not yet reached the age of puberty. But if a person has reached the age of puberty while he is in sound mind and not insane, then he is held accountable for his deeds and is addressed by the rulings of the Sharee'ah.
You being determined to get rid of the debt and become righteous is something praiseworthy and you should thank Allah for guiding you to this. The Prophet said: “A believer is created and he is tried (afflicted), repentant, and forgetful; if he is reminded, he remembers (he takes heed).” [At-Tabaraani, and Al-Albaani classed it as Saheeh]
Al-Manaawi said: “It means that Allah tests him with afflictions and sins, time and time again; the one who is afflicted and tested refers to the one who is afflicted much. The term “he is repentant and forgetful, if he is reminded, he remembers”: means that he repents, then he forgets and returns to the sin, and then he remembers and repents…” [End of quote]
Allah knows best.