The phrase "son man" typically refers to a young man who is still under the guidance of his father. While not necessarily a negative term, it carries a connotation of youth and immaturity. Some synonyms for "son man" might include "youth," "adolescent," "boy," "youngster," or "junior." These all carry similar connotations, though some might sound more formal or dated than others. The context in which the term is used will typically determine which synonym is most appropriate, but it's worth considering the nuances of each to make sure you're conveying the right meaning.