(Exodus 36:4) "See, the LORD has called by name" etc. "Each man from his own work which they were doing." It is written "Bezalel son of Uri son of Hur of the tribe of Judah," and it is written (1 Chronicles 2:19) "And Azubah died, and Caleb took to himself Ephrath, and she bore him Hur." Now when Bezalel made the Tabernacle, how old was he? Thirteen years old, for it is written "each man from his own work." And it was taught: in the first year Moses made the Tabernacle; in the second he set up the Tabernacle and sent the spies. And it is written (Joshua 14:6-7) "Forty years old was I when Moses the servant of the LORD sent me." How many years are there? Forty. Subtract fourteen, which was Bezalel's age - twenty-six remain. Subtract two for the three intercalated years - twenty-four remain. It is found that each one fathered a child at the age of eight. (Exodus 36:6-7) Levi taught: "Each man from his own work" - from his own work he makes, and he does not make from his fellow's work.
Reckoning the Young Age of Bezalel When He Built the Tabernacle
Yalkut Shimoni on Torah 413:1
(שמות לו ד) רְאוּ קָרָא ה' בְּשֵׁם וְגוֹ'. אִישׁ אִישׁ מִמְּלַאכְתּוֹ אֲשֶׁר הֵמָּה עֹשִׂים. כְּתִיב בְּצַלְאֵל בֶּן אוּרִי בֶן חוּר לְמַטֵּה יְהוּדָה, וּכְתִיב (דבהי"א ב, יט) "וַתָּמָת עֲזוּבָה וַיִּקַּח לוֹ כָּלֵב אֶת אֶפְרָת וַתֵּלֶד לוֹ אֶת חוּר", וְכִי עֲבַד בְּצַלְאֵל מִשְׁכָּן בַּר כַּמָּה הֲוָה, בַּר תְּלֵיסַר שָׁנֵי כְּתִיב אִישׁ אִישׁ מִמְּלַאכְתּוֹ, וְתַנְיָא, שָׁנָה רִאשׁוֹנָה עָשָׂה מֹשֶׁה מִשְׁכָּן, שְׁנִיָּה הֵקִים מִשְׁכָּן וְשָׁלַח מְרַגְּלִים, וּכְתִיב (יהושע יד, ו ז) "בֶּן אַרְבָּעִים שָׁנָה אָנֹכִי בִּשְׁלֹחַ מֹשֶׁה עֶבֶד ה' אֹתִי", כַּמָּה הָוְיָא לְהוּ, אַרְבָּעִים, דַּל אַרְבָּסַר דַּהֲוָה בְּצַלְאֵל, פְּשׁוּ לְהוּ עֶשְׂרִין וְשִׁית, דַּל תַּרְתֵּי דִּתְלָתָא עִבּוּרֵי, פְּשׁוּ לְהוּ עֶשְׂרִים וְאַרְבַּע, אִשְׁתַּכַּח דְּכָל חַד וְחַד בַּר תְּמָנֵי אוֹלִיד. (שמות לו ו-ז) תָּנֵי לֵוִי, אִישׁ אִישׁ מִמְּלַאכְתּוֹ, מִמְּלַאכְתּוֹ הוּא עוֹשֶׂה וְאֵינוֹ עוֹשֶׂה מִמְּלֶאכֶת חֲבֵרוֹ.