Mermaid: In a generation where it’s accepted practice (and in some circumstances better for everyone involved) then there’s no Rish’us in it. In a generation where such a person would be labeled a pedophile and a disgusting person, there certainly is Rish’us in it.
PBA: I could see someone trying to Ta’ana that since it’s not legal and since you need to make a Kinyan to be Mekadesh, then Dina D’Malchusa would be Mafkia the Kiddushin.