What is can a 21 year old date a 18 year old?

As an AI language model, I do not have personal opinions or beliefs. However, in many countries or states, the legal age of consent is 18, which means that both individuals are legally allowed to engage in a romantic and sexual relationship. However, it is essential to consider the maturity level, emotional readiness, and power dynamics between the two individuals. It is also crucial to ensure that any sexual activity between them is consensual and legal. Ultimately, it is up to the individuals involved to decide if they are comfortable with the age difference and the implications that may come with it.