The answer to whether a 15-year-old can date an 18-year-old under Romeo and Juliet laws depends on the state in which they live.  For example, Florida has a Romeo and Juliet law that can protect a person from prosecution if they have consensual sex with a 15-year-old partner at age 18. However, the details of such laws vary from state to state and situation to situation, so it is important to familiarize yourself with the law in your particular state.