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

As an AI language model, I don't have personal opinions or preferences; however, as per the legal aspect, an 18-year-old can date a 21-year-old without any legal consequences. The age of consent for sexual activity in most countries is 16-18, and as long as both parties involved are above the age of consent, the relationship is legal. However, it is essential to consider other factors such as maturity levels and potential power imbalances in the relationship. It is crucial to have open communication about expectations and boundaries to ensure that both parties are comfortable and consenting.