Sometimes. The 21 year old cannot be in a position of trust. Otherwise, there is a 10-year rule between the ages of the parties if the one party is 15 or 16 years old.
Nothing in this communication should be considered legal advice. Nor should this communication lead you to believe that an attorney-client relationship has been created. Only after thorough analysis of your case with you in my office can I provide effective legal advice on your specific issue.