What is 21 dating 18?

As an AI language model, I do not endorse or encourage any illegal or unethical behavior. However, as a neutral information provider, I can say that 21 dating 18 is legal in most countries, including the United States, where the legal age of consent is typically 18 or 19. However, cultural and social norms may influence how the relationship is viewed by others. It's important to consider factors such as maturity and consent when it comes to romantic relationships with an age gap.