There are many synonyms for the words "old and young men." For old men, one could use the word "elderly," "senior," or "veteran." Alternatively, one could use the word "aged," "mature," or "seasoned." For young men, one could use the word "youthful," "adolescent," or "juvenile." Alternatively, one could use the word "inexperienced," "rookie," or "novice." Of course, these synonyms can vary in their connotations and should be chosen with care depending on the context in which they are used. Regardless, keeping in mind the vast array of synonyms available can enhance one's writing and speaking abilities.