Here's my idea: if even one bishop/Cardinal of a large US Catholic archdiocese were to announce at the beginning of the New Year: “If the Catholic Church were to marry only perfect people, we'd be performing no weddings. However, we can and should insist that engaged couples at least publicly be committed to being sincere Catholics. You should not be living together before you get married if you want to get married in the Catholic Church. If you are living together, separate immediately. If your attitude is, ‘We just can lie about it’, ask yourselves why you have such an adolescent attitude about the most important commitment you'll make in your life. We're not going to be following people home from their jobs to find out where they ‘realy’ live, but if you admit you are living together, or fill out the same address on forms, we will rescind permission to marry in our archdiocese. Also, to marry in the Catholic church means you are committed to attend church every Sunday, to raise your children Catholic and bring them to church every Sunday, and to send them to Catholic school or enroll them in CCD. If you do not pledge to do all of those things, we will not marry you in our archdiocese. Yes, you can lie about those things. Again, I ask you, why would you make the most important commitment of your life with a lie?”
The above may have an indirect effect on what the non-Muslim population, but it may start a wave of people who stop this years of living together nonsense, which has people deferring marriage indefinitely.
Birth control and easy access to abortion have more to do with ‘living together’ and deferring marriage than almost anything. This allows single women to sleep around as if they where men. Women control the sex act and if they didn't allow men to have sex with them without a commitment, men would be getting married much earlier. Couple that with the insanity of the need for a college education and women needing a career (mainly due to massive confiscatory taxes) and many people delay getting married until after thirty.
Here is a simple fact. Getting pregnant after 30 and especially 35 is very difficult for most women. The female body was intended to have children early and often but mostly early, before thirty and even better before 25.