Midrash for Yevamot 124:6

“In the morning, sow your seed, and in the evening do not rest your hand, as you do not know which will succeed, whether this or that, or whether they both alike will be good” (Ecclesiastes 11:6).
“In the morning, sow your seed” – Rabbi Eliezer and Rabbi Yehoshua: Rabbi Eliezer says: If you sowed early in the season, sow [another field] late in the season, as you do not know which will endure for you, the early or the late. “As you do not know which will succeed, whether this or that.”
Rabbi Yehoshua says: If you married a woman in your youth and she died, marry in your old age. If you had children in your youth, you should have children in your old age, as it is stated: “In the morning, sow your seed, and in the evening do not rest your hand, as you do not know which will succeed, whether this or that.”
Rabbi Yishmael and Rabbi Akiva: Rabbi Yishmael says: If you studied Torah in your youth, study in your old age, as you do not know which Torah will endure, that of your youth or that of your old age, “or whether they both alike will be good.” Rabbi Akiva says: I had twelve thousand students from Gevat to Antipatris, and they all died during my lifetime, between Passover and Shavuot. Ultimately, seven promulgated my [Torah],³⁵Seven students whom I taught in my old age were responsible for dissemination of my Torah. and these are they: Rabbi Yehuda, Rabbi Neḥemya, Rabbi Meir, Rabbi Yosei, Rabbi Shimon ben Yoḥai, Rabbi Eliezer son of Rabbi Yosei HaGelili, and Rabbi Yoḥanan the cobbler. He said to them: The first ones died only because they were begrudging to each other regarding their Torah. Do not be like that. They quickly rose and filled all of the Land of Israel with Torah.
Rabbi Natan interpreted the verse regarding a woman. If you married a woman in your youth, marry in your old age. Why? It is because you do not know which children will endure for you, whether it is those of your youth or of your old age, or “whether both alike will be good.”