The rules for the CRC state, "Individuals must be at least 21 years of age for club membership or access." In addition they state, "Alcoholic beverages will not be served to anyone under 21 years of age. Local age restrictions apply in non-U.S. locations." Finally you are allowed guests as follows, "A member may bring two guests into the Crown Room Club, provided that Delta determines that adequate space exists.
Guest privileges apply only when the visitors accompany the member."

I seriously doubt that DL would not mail you a PM card if you reach that level. Therefore, what rule states that you cannot invite a person (guest) over the age of 21 into the CRC with you? If you obtain PM status, and you are chaperoned by an adult, IMHO they should not deny you entry.