The expression “from my youth” in Mark and Luke does not have to conflict with the fact that Matthew speaks of the man as a “young man.” The word for “young man” (νεανίσκος) points to the period of life of the young man (sometimes specified as the age of twenty-one to twenty-eight years). The expression “from youth” (ἐκ νεότητός) compares the period of youth with the later time of life: it can go back to the earliest youth. In short, the young man will have been about twenty-five years old and has kept the commandments from his youth (twelve/thirteen years).1
20 And he said to him, “Teacher, all these I have kept from my youth.”