Komentarz do Diwrej ha-jamim I 2:20

And Hur begot Uri, and Uri begot Bezalel Figure that each of them was less than eight years old when they begot, for Caleb was forty years old during the episode of the spies, as it is written (Jos. 14: 7): “I was forty years old when [Moses, the servant of the Lord] sent, etc.,” and at that time they all were already born, for the Tabernacle that Bezalel made had been erected. Caleb was eight years old when he begot Azuba Ishah, nine years old when he begot Jerioth, and after the death of Azubah, his wife, he took Ephrath, and she bore him Hur in the following year, making him ten years old, and Hur was eight years old when he begot Uri, and Uri was eight years old when he begot Bezalel, thus making 26 years, and it is written (Exod. 36:1): “and every wise hearted man,” and a man is not less than thirteen years old. So Bezalel was thirteen years old when he made the Tabernacle. Thus, we have forty years less one. We find that each one of them was less than eight years old when they begot children, and so it is explained in Chapter “Ben sorer umoreh“ (Sanh. 69a). According to the Midrash, they begot at the age of six.