Why is it an unenforceable law? The reason you haven’t encountered one yet is because it was socially unacceptable and they would be prosecuted under other laws.
There is a movement to force acceptance and legalization of this activity. This law is intended to counter that move.
Its intended to protect the children, not the 67 year old.
It is not the government's job to protect children. That is the job of parents. Most of us get really upset when the government takes over the role of parent. There are laws against pedophiles but they still attack unprotected children. Parents or responsible adults protect children.