II Samuel 5:4 Midrash

בֶּן־שְׁלֹשִׁ֥ים שָׁנָ֛ה דָּוִ֖ד בְּמָלְכ֑וֹ אַרְבָּעִ֥ים שָׁנָ֖ה מָלָֽךְ׃

David was thirty years old when he began to reign, and he reigned forty years.

Read midrashic interpretation of II Samuel 5:4: and classical rabbinic exegesis.