Is there an age that people should stop having children?
Yes. Absolutely. When they die.
(The tzibbur laughed)
You think I’m laughing? I’m not laughing. Look at the Chofetz Chaim. His wife died when he was an elderly man and he married again and had a son. He had a son. The Gemara says this. “Ha’yu lo banim bi’yalduso, yi’hiyu lo banim bi’ziknuso.” (Yevamos 62b).
The Rambam says as follows. Listen to the Rambam’s words. He’s talking about person marrying and having children in his old age and he says, “Kol ha’mosif nefesh achas mi’Yisroel, ki’ilu banah olam” (Hilchos Ishus 15-16). If you add another child into the world, you’ve added a whole new world. It’s not one child! It’s an olam malei! A whole world! Because from that one child, there will be children and grandchildren. And great-grandchildren. Thousands and thousands of people will come from that one child. And it’s to your credit. “Ki’ilu banah olam.” You’ve built a whole world!
That’s why a Jew who kills another Jew, even by accident – if he was a careless driver, let’s say – he’s not just a murderer of one person. “Damo u’dam zro’osov, ti’lu’yin bo, ad sof kol ha’doros.” “I didn’t do that,” he says. Yes, you did. He killed a Jew by driving carelessly. He killed tens of thousands of Jews that could have come out of this one person.
And that’s how important it is to add on one more person to the Jewish nation. That person is an olam malei, says the Rambam. “Kol ha’mi’abeid nefesh achas, ma’alin a’lav ki’ilu ibeid olam malei. Vi’chol ha’mikayeim nefesh achas, ki’ilu ki’yeim olam malei” (Rambam Hilchos Sanhedrin 12-3). That’s how the Rambam connects the din of hariga with having children in one’s old age. Because bringing a child into this world is like building an olam malei.