Can one secretly marry a girl who has been harmed until the young man is able to assume responsibility?

Both of you must engage in sincere repentance. Repentance is achieved through sincerity, remorse, and a firm resolve not to return to the sin. Repentance must occur at a time when Allah accepts it. It is not permissible for you to marry her until after sincere repentance from zina (fornication/adultery). As for a secret marriage, there is no harm in it if it is done with the guardian's consent and the presence of two witnesses, provided it is not publicized. However, marriage is not valid without the guardian's knowledge and consent, for the Prophet, peace and blessings be upon him, said: "There is no marriage without a guardian." As for your family, their permission is not a prerequisite for your marriage.