Manga wo Yomeru Ore ga Sekai Saikyou: Yome-tachi to Sugosu Kimama na Seikatsu

The other world I reincarnated to was a world that will enable you to use magic after reading a Grimoire. And the Grimoire's contents are... manga! This world's people would take around one year to read one Grimoire (manga), but it's just manga to me, so it doesn't even take an hour. Having become the world's strongest master mage at 6 years old after interpreting and understanding all kinds of Grimoires, I welcomed brides that were also 6 years old, and started living a carefree life!

(Source: Shueisha, translated)