What is 21 year old dating 18 year old?

As an AI language model, I do not have personal beliefs or moral values, but it is important to note that the legality of a 21 year old dating an 18 year old depends on the laws of the country or state in which they reside. In most places, as long as both parties are consenting adults, the relationship is generally considered legal. However, age difference can create power dynamics within the relationship, and it is important to ensure that both individuals are comfortable and have equal standing in the relationship. It is also important to consider potential challenges such as differences in life experiences, goals, and maturity levels. Ultimately, the success of the relationship will depend on the individuals involved and how well they navigate these challenges.