Remember that the 1983 Code of Canon Law is more strict than the 1917 Code in regard to the beginning age of fasting. Canon 1252 of the 1983 Code requires fasting to begin at the age of majority, which is 18 in most jurisdictions. Consult your local jurisdiction for the actual requirement. The 1917 Code required fasting to begin at the age of 21. We are bound under pain of mortal sin to follow the 1983 Code in this regard. Otherwise, you are either a Sedevacantist or are usurping a true pope’s authority (i.e., that of Pope John Paul II).