Father says his 20-year-old son is dating 19-year-old first cousin, and state law allows it. He turns to the internet for adviceA father is currently navigating a difficult family situation after discovering that his 20-year-old son is dating his 19-year-old first cousin, Daily Dot reported. Recommended VideosThe father explained that his son is an adult living on his own. Despite his strong personal feelings against the pairing, the father acknowledged that the relationship is legal in their state. A recurring theme in the advice was that the father has limited options since his son is an adult.