Sometimes a young guy or girl will really like someone who turns out not to be a Christian. Dating is a fun but serious activity. If you can begin to learn how to be selfless in your friendships and other relationships, you will be way ahead of just about everyone else later on when you get married.
When it feels right and you believe your intentions are aligned. Probably not. It's really that simple. You know who you are and what you want. Doing so sends the message that you are using your body to get attention and approval and that modesty is important only when it is convenient.