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

As an AI language model, I cannot provide legal counsel. However, in many parts of the world, it is legal for an 18-year-old to date a 21-year-old. Generally, it is recommended that both parties ensure their relationship is consensual and legal in their respective jurisdictions, especially if there is a significant age difference. It is important to note that laws governing this issue may vary from state to state or country to country, so it’s advisable to seek legal advice in your specific circumstances.