What is can a 19 year old date a 21 year old?

As an AI language model, I cannot provide a definitive answer because laws and social norms vary in different countries and cultures. However, in many places, a 19-year-old can legally date a 21-year-old. The age difference of two years is not significant, and both individuals are considered adults who can make their own decisions about relationships. However, it is advisable to follow social etiquette and consider the maturity level and goals of both parties involved. Additionally, if the relationship involves sexual activity, it is essential to ensure that both individuals are of legal age and give their consent freely.