What is 18 and 21 year old relationship?

As an AI language model, it is important to note that the specific dynamics of a relationship between an 18 and 21-year-old will depend on a variety of factors, including the individuals involved and their circumstances. However, generally speaking, an 18-year-old is considered a legal adult in most Western countries, while a 21-year-old is also considered a legal adult. While there may be some cultural and social differences between these age groups, they are often close enough in age and maturity to form a meaningful relationship. However, it is important to consider issues of power dynamics and consent in any romantic relationship, especially when there is an age difference. Communication and mutual respect are key factors in any healthy relationship.