You did not clarify what you mean by "dating." If the minor is under fifteen it is illegal for them to have any sexual contact. If she is fifteen and he is eighteen, he can still get in trouble. If she is sixteen, he cna still get introuble, but police rarely enforce the law, if she seems to be consenting. If she gets pregnant, his parnts may have to pay chidl support if he is living at home, or if one of his parnets is getting child support from the other parent. If ther is not sexual contact, and the minor's parents have not forbade thier child from socializing with the eighteen year old, there appears to be no law against them dating.

Good luck